AIARCH 3, 1905.] than begun the scientific investigation of a field which offers the widest opportunities for results. Not only does it seem probable that practically new linles of business are to be created by botany, but the improvement in old methods which have been maintained for centuries simply because 'our fathers' did that way, has already demonstrated to the most conservative that the scientific botanist, true to type, is a man of immense practical value to the farmer, the manu- facturer, the engineer and the world at large. May we none of us, by our work or our words, retard the rapid advance now being made, along both pure and practical scien- tific lines, of our chosen science-botany. GEORGE T. MOORE. BUREAU OF PLANT INDUSTRY. AMERICAN ASSOCIATION FOR THE AD- VANCEMENT OF SCIENCE. SECTION B, PHYSICS. THE annual meeting of Section B, Phys- ics, of the American Association for the Advancement of Science, in affiliation with the American Physical Society, was held in Philadelphia on December 28, 29 and 30, 1904. The attendance was represen- tative in an unusual degree of the physi- cists of the entire country, including not only those from many important institu- tions of the east, but also from the south, the west, and from California. The av- erage attendance was nearly one hundred. The retiring vice-president, Edwin HI. I-Tall, introdueed the presiding officer, Pro- fessor 'W. F. Ma.gie, of Princeton Univer- sity, the vice-president of Section B. The other officers of the section who were in attendanee were Dayton C. Miller, secre- tary; Henrv Crew, couneillor; A. W. Good- speed, member of the general committee; and the following members of the sectional committee, W. F. Magie, E. H. Hall, D. C. Miller, E. L. Nichols, F. E. Nipher, G. F. Hull, A. G. Webster, D. B. Brace. For the next meeting, to be held in New Orleans, beginning December 29, 1905, the presiding vice-president is Professor Henry Crew, of Northwestern University. The other officers for the New Orleans meeting, so far as now determined, are: Retiring Vice-President W. F. Magie. Members of the Sectional Committee-Heiiry Crew, WV. F. Magie, D. C. Miller, E. L. Nichols, F. E. Nipher, G. F. Hull and A. G. WVebster. Scretary-Dayton C. Miller, Case School of Applied Science, Cleveland, Ohio. On Thursday the retiring vice-president, Professor E. H. Hall, of Harvard Univer- sity, gave an address on 'A Tentative The- ory of Thermoelectric Action.' This im- portant paper, which is printed in full otherwhere in this journal, was listened to by an unusually large audience. Twenty-two papers were read before Sec- tion B, all of which were of such impor- tance that it was generally expressed that this meeting was one of the most valuable that Section B has ever enjoyed. The sub- jects may be classified as follows: on light, nine papers; on electricity, five; on meteor- ology, two; and on general subjects, six papers. Papers on related subjects were grouped together more than had been usual before, and ample time was allowed for discussion. This arrangement added to the value, as well as to the enjoyment, of the sessions. Beginning on Friday, December 30, the sessions were in charge of the American Physical Society; a large number of valu- able papers were read, an account of which is given in the report of the Physical So- ciety. The abstracts of the papers read before Section B are given below. 7ote on tl e Mirror-Telescope-Scale Method: GEORGE F. STRADIAING, Manual Training School, Philadelphia. SCIENCE. 333 on January 12, 2021 http://science.sciencemag.org/ Downloaded from
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AIARCH 3, 1905.]
than begun the scientific investigation of afield which offers the widest opportunitiesfor results. Not only does it seem probablethat practically new linles of business are tobe created by botany, but the improvementin old methods which have been maintainedfor centuries simply because 'our fathers'did that way, has already demonstrated tothe most conservative that the scientificbotanist, true to type, is a man of immensepractical value to the farmer, the manu-facturer, the engineer and the world atlarge.May we none of us, by our work or our
words, retard the rapid advance now beingmade, along both pure and practical scien-tific lines, of our chosen science-botany.
GEORGE T. MOORE.BUREAU OF PLANT INDUSTRY.
AMERICAN ASSOCIATION FOR THE AD-VANCEMENT OF SCIENCE.
SECTION B, PHYSICS.
THE annual meeting of Section B, Phys-ics, of the American Association for theAdvancement of Science, in affiliation withthe American Physical Society, was heldin Philadelphia on December 28, 29 and30, 1904. The attendance was represen-tative in an unusual degree of the physi-cists of the entire country, including notonly those from many important institu-tions of the east, but also from the south,the west, and from California. The av-erage attendance was nearly one hundred.The retiring vice-president, Edwin HI.
I-Tall, introdueed the presiding officer, Pro-fessor 'W. F. Ma.gie, of Princeton Univer-sity, the vice-president of Section B. Theother officers of the section who were inattendanee were Dayton C. Miller, secre-tary; Henrv Crew, couneillor; A. W. Good-speed, member of the general committee;and the following members of the sectionalcommittee, W. F. Magie, E. H. Hall, D. C.
Miller, E. L. Nichols, F. E. Nipher, G. F.Hull, A. G. Webster, D. B. Brace.For the next meeting, to be held in New
Orleans, beginning December 29, 1905, thepresiding vice-president is Professor HenryCrew, of Northwestern University. Theother officers for the New Orleans meeting,so far as now determined, are:
Retiring Vice-President W. F. Magie.Members of the Sectional Committee-Heiiry
Crew, WV. F. Magie, D. C. Miller, E. L. Nichols,F. E. Nipher, G. F. Hull and A. G. WVebster.Scretary-Dayton C. Miller, Case School of
Applied Science, Cleveland, Ohio.
On Thursday the retiring vice-president,Professor E. H. Hall, of Harvard Univer-sity, gave an address on 'A Tentative The-ory of Thermoelectric Action.' This im-portant paper, which is printed in fullotherwhere in this journal, was listened toby an unusually large audience.
Twenty-two papers were read before Sec-tion B, all of which were of such impor-tance that it was generally expressed thatthis meeting was one of the most valuablethat Section B has ever enjoyed. The sub-jects may be classified as follows: on light,nine papers; on electricity, five; on meteor-ology, two; and on general subjects, sixpapers. Papers on related subjects weregrouped together more than had been usualbefore, and ample time was allowed fordiscussion. This arrangement added to thevalue, as well as to the enjoyment, of thesessions.
Beginning on Friday, December 30, thesessions were in charge of the AmericanPhysical Society; a large number of valu-able papers were read, an account of whichis given in the report of the Physical So-ciety.The abstracts of the papers read before
Section B are given below.
7ote on tl e Mirror-Telescope-ScaleMethod: GEORGE F. STRADIAING, ManualTraining School, Philadelphia.
Let a ray of light of fixed direction fallupoIn a muirror turning about a verticalaxis. The reflected ray is received upona plane. If the incident ray passesthrough the vertical axis, and this axis liesin the plane of the mirror, and the planeon which the reflected ray falls is parallelto the mirror-plane, the curve traced bythe spot of light as the mirror turns is ahyperbola. Discussion of another ease.
Somc Convenient Laboratory Apparatus:hIORACE C. RICHARDS, University ofPennsylvania.I. An Apparatus for Quickly Washing
an-d Filling Vessels with Small Openings.-It consists of a small glass cylindermiiounted on a suitable stand and providedwith three outlets, one leading to the vesselwhich is to be filled, one to that containingthe liquid, and the third to an aspiratorthrough a trap. The liquid is first drawnup into the cylinder and then, by inter-mittent working of the aspirator, is driveninto the vessel. A similar process emptiesthe vessel and carries the liquid over intothe trap. For mercury, etc., the form isslightly modified so as to prevent loss ofthe liquid.
II. A Simple Automatic MercurylWasher.- Mercury is raised by an as-pirator into a vessel placed above a verticaltube filled with dilute nitric acid. Whent.he vessel is filled, the aspirator is auto-matically shut off and at the same timeair is admitted by a pair of valves operatedby a float. The mercury then filtersthrough a small valve in the bottom of thevessel and falls in small drops through thecolumn of acid. It is then returned to thereservoir from which it was drawn and sois passed around through the acid as oftenas is desired, the aspirator being set inaction again when the upper vessel isnearly empty.
The Double Suspensiont Penidulum for De-termining the Absolute Vaclue of theAcceleration of Gravity: R. S. WOOD-WARD, Carnegie Institution.This papc-r describes an apparatus spe-
cially designed to avoid the difficultiespresented by knife-edge pendulums and tosecure a degree of precision in absolutemeasures of the acceleration gravity com-parable with the precision already attainedin relative measures.
Heat Insulation of Observatory Domes,Laboratories an?d Other Buildings.DAVID TODD, Amherst College.To prevent excessive heat accumulation
in the new observatory domes at Am-herst waste granulated cork is put in be-tween the interior galvanized iron sheath-ing and the exterior wood boarding onwhich the copper roof is fastened. Oneand one half to two inches of cork is suffi-cient to keep interior iron always cool tothe touch, no matter how hot the coppergets when the sun is shining normallyupon it. Mineral wool would be nearerfire-proof and equally good insulation, butadds more weight. Numerical tests willbe submitted.The Relation Between Air Pressure and
Velocity. FRANCIS E. NIPHER, Washing-ton University. To be published inthe Transactioits of the Academy of Sci-ence of St. Louis.The paper describes a method of de-
termining the constant in the equationP kv2 when the air blows into the openend of a tube collector. The tube wasbolted to a small pulley on a shaft whichcould be run at various speeds. The openend was 36 inches from the center of thepulley, and the plane of the opening couldbe set at any angle with the circular pathwhich it describes. When at right anglesto the path the air within the tube is foundto be in equilibrium during rotation. The
pressure required to balance the out.wardradial tendency is equal to the pressuredue to the wind at the open end of thetube. When this condition is imposed inthe equation the value of k is obtained interims of temperature, barometric pressureand velocity. The value is practically in-dependent of v for velocities less than 100miles per hour.
1'ihe Temperatutre and Drift of the Air atGreat Heights above the American Con-tinent, Obtained by Means of Registra-tion Balloons. (Preliminary Report.)A. LAWRENCE ROTCH, Director of BlueHill 1\Ieteorological Observatory.Although the meteorological conditions
of the lower two or three miles of air havebeeni investigated by means of kites at BlueHill Observatory during the past ten years,no observations have been made at greaterheights in this country. Through coopera-tioni witlh the imanagement of the St. LouisExposition, the author obtained such ob-servations by means of ballons-sondes;fourteen of these balloons carrying self-recordino instruments were despatchedfrom St. Louis and all were recovered withten records of barometric pressure and airtemperature. From the barometric ree-ords the maximum height attained wasfound to be about 51,000 feet, where thetemperatiire was 68° F. below zero onSepteinber 23. At a height of about 45,500feet (the maximum of the second series ofexperimiientss) the temperature was -72°F. on December 2, the lowest temperature,-76° occurring at a height of about33,000 feet on November 26. The direc-tion and velocity of the upper air currentswere indicated approximately by the placesand timies at which the balloons fell. Thevelocitv twice exceeded 100 miles an hourand(t all the balloons (excepting one whichdid not rise out of the surface current)drifted towards the east, in general diverg-
ing from the areas of low barometric pres-sure at the ground.An account of these experiments will
be published in full in the Annals of theHarvard College Observatory, Vol. LVIII.,Part II.
Optical Refraction in the Lower Atmos-pheric Strata, as Affected by theMeteorological Conditions. (Prelimi-nary Report.) A. LAWRENCE ROTCH,Director of Blue Hill Meteorological Ob-servatory.The variation in refraction has generally
been attributed to the differences in thetemperature of superposed strata of air,but there have been few investigationsupon the effeet of the daily changes inmeteorological conditions. Accordingly,during two years, observations were madethree times a day with a precise level, onthe summit of Blue Hill, of the apparentangular depression of a lighthouse in Bos-ton harbor, fourteen miles distant and550 feet below the hill, the temperatureshere and over the water being known.Since the temperature of the air over theocean is more uniform than that over theland, there is a large annual period in theirdifference, but no relation between thesevertical gradients and the observed refrac-tion is evident, nor do the monthly ex-tremes appear to be connected with thecorresponding gradients of temperature.This indicates that there are other con-trolling influences and these are now beingsought. The investigation will be pub-lished in Vol. LVIII., Part II., of theAnnals of Harvard College Observatory.
Experimtental Sttdy of the Use of TWestonInstrum ents for Ballistic Magnetic Test-ing. ALBERT F. GANZ, Stevens Instituteof Technology.At various times it has been either
claimed or disputed that a damped gal-vanometer in which the damping force is
proportional to the velocity of the. movingsystem may be used for ballistic magnetictesting. In the Physical Review, of March,1903, there is an article by 0. M. Stewartin which it is shown mathematicallythat such a damped galvanometer con-forms to the ordinary law of the undampedballistic galvanometer. It is also statedin this article that an ordinary Westonammeter wit.hout its shunt or a Westonvoltmeter without its series resistance maybe used for determining permeability andhysteresis curves by the ballistic method.The experiments to be described in this
paper were undertaken las,t spring by twosenior students, Mr. E. E. Greve and Mr.A. R. Barkus, under the direction of thewriter, for the purpose of comparing thepermeability and hysteresis curves ob-tained by means of ordinary Weston in-struments, with the curves obtained bymeans of a slow-period undamped ballisticgalvanometer. It was found that thecurves for a laminated iron ring obtainedwith an ordinary West-on instrument fellabout three per cent. below the curve ob-tained with t.he ballistic galvanometer. Itwas also found that the permeability curvefor a solid iron ring (cross-section 1. sq. in.mean diam. 7 in.) obtained with an or-dinary WNeston instrument fell over ten percent. below the curve obtained with the bal-listic galvanometer. The cause of this fall-ing below is undoubtedly that the time ofthe first swing of the ordinary Weston in-strument is too short to take account of allthe change in the magnetic flux which (ce-curs. The Weston Instrument Co. thenconstructed a special instrument having agreater moment of inertia and more mag-netic dampingo than their ordinary instru-men-ts, and having, therefore, also a muchlonger time for its first swing. This newinstruiment was found to give a permea-bility curve for the laminated ring whichagreed exactly with the curve obtained
with the ballistic galvanometer. For thesolid ring the permeability curve was still,however, several per cent. below the curveobtained with the ballistic galvanometer.In order to make a direct reading, magneticflux meter out of this instrument ten yardsof flexible cord were taken to be used for asecondary coil, and a resistance was addedto the instrument, and this was adjustedso that the instrument would indicate theflux in kilomaxwells changed per turnusing this secondary. This instrumentwas, therefore, called a 'W\Teston Maxwellmeter.' This Maxwell. meter has been con-siderably used in the laboratory ofStevens Institute for obtaining magnetiza-tion curves, mea.suring leakage coefficients,etc., and has been found extremely useful.The Weston Co. are now constructing asecond special instrument having a stillslower period, which is expected to giveaccurate results as well for solid iron sam-ples as for laminated ones, and this willbe a direct reading, portable and perman-ent Maxwell meter having a uniform scale,wvhich will be generally useful for all kindsof magnetic testing and which can be useddirectly without previous calibration.Owing to the slow period of these specialinstruments the extent of their first throwscan be very accurately noted.
lieasurement of the Thompson Thermo-elcctric Effect in Iron. EDWIN H. HALL,hIarvard Univer-sity.
Description and Demonstration of thePoulsen Telegraphone. Z. B. BABBITT,New York; Introduced by Arthur W.Goodspeed.The principles involved in the Poulsen
telegraphone and the practical constructionof the apparatus were explained. The re-production of human speech was thendemonstrated.
Circular Dichroism in Natural RotarySolutio'ns. D. B. BRACE and W. P.McDowELL, University of Nebraska.
Electric Double Refraction in Liquids Un-der Low Electric Stresses, and also at theBoiling Point. D. B. BRACE, G. W.ELMEN and L. B. MORSE, University ofNebraska.
The Electromagnetic Theory and theVelocity of Light. HENRY T. EDDY,University of Minnesota. (To be pub-lished in the Physical Review.)Mr. Mills has recently published a
paper* in which he has given the resultsof measurements made by him of the in-crease in the velocity of circularly polar-ized light in bisulphide of carbon alongthe lines of force in a magnetic field. Em-ploying circularly polarized light, he wassuccessful in obtaining a difference of oneor miore wave-lengths between two rayseircullarly polarized in opposite senses,one ray having its velocity increased whilethe other was decreased, and this was ob-tained with apparatus with which no dif-ference whatever was observable in easeof plain polarized rays.The apparatus mentioned is a form of
interferometer devised by Professor Mor-ley and paid for by a grant made by theAmerican Association for the Advance-ment of Science for the purpose of investi-gating certain points to which the presentwriter had taken exception in the theory ofthe Faraday effect as developed by Pro-fessor Rowland, t who had attempted toaccount for the twisting of the plane ofpolarization of plane polarized light whilebeing propagated along the lines of forcein a magnetically active medium by theaction of the Ilall effect in the medium.As just stated, the present writer foundhimself unable to agree with that part of
* Phys. Rev., Vol. XVIII., p. 65, Feb., 1904.t Am. Jour. Math., Vol. 3, p. 109, 1880.
337
Professor Rowland 's most valuable theo-retical treatmnent of the Hall effect whichrelated to rotary polarization. After afull presentation of the theoretical ques-tions involved at the Toronto meeting ofthe American Association for the Advance-ment of Scienace, in 1889, the apparatuswas constructed, and after many delays afinal report was presented to the AmericanAssociation for the Advancement of Sci-ence, at the Boston meeting, August, 1898.'The report was duly published* and con-tains, first, the present writer's theoreticaldevelopments and computations as to thepossible increase or decrease in! velocity tobe looked for in case of magnetic twistingof the plane of polarization, and second,a full description by Protfessor Morley ofhis apparatus and a detailed account ofthe experimental work by Professors Mor-ley and Miller, who worked in collabora-tion. No experimental change in thevelocity of plane polarized light could bedetected with this' apparatus, and thenumerical computations just mentionedshowed in fact the possible change in thevelocity to be too minute to be detected bythe apparatus as used. Although such isthe fact with plane polarized light, the ex-periments of Mr. Mills show that such isnot the fact with circularly polarized light.Mloreover, it will be shown theoreticallythat in case of circularly polarized lightthe amount of change in velocity due tothe magnetic field is expressible as a lowerpower of small quantities, than in case ofplane polarized light, and consequently themagnitude of the change in the formercase is large compared with the latter, andin fact varies as the square of the latter;and while the latter may be quite beyondthe range of observation, the former maybe, well within it, as the experiments ofMr. Mills have proven.
In view of this it is the aim of this paper* Phys. Rev., Vol. VII., p. 282, December, 1898.
in the first place to rediscuss the questionsat issue and point out, more in detail thanheretofore how, a,ccording to elementarytheory, the velocities of plane and circu-larly polarized rays in any optically ormagnetically active medium must be neces-sarily related to each other, and how, ac-cording to elementary theory, it is impos-sible that Professor Rowland's equationscan represent a, twisted plane polarizedray.
In the second place, it will be shownhow these velocities in the magneticallyactive field are related to the velocity inzero field according to the several pro-posed hypotheses. WATere it possible tomake this comparison experimentally, weshould have a test as to the validity ofthe proposed hypotheses, but such test isas yet beyond reach by reason of the small-ness of their differences.An attempt i.s made, in the third place,
to show that a moderate degree of absorp-tion would exert a negligible influence inmodifying the results already developedfor perfectly transparent media.The conclusions arrived at in this paper
may be briefly stated as follows:1. The increase or decrease in the veloc-
ity of circularly polarized light observedby Mr. Mills, and previously by ProfessorBrace, are perfectly in accord with and anecessary consequence of the elementarytrigonometrical equations expressing thepropagation of twisted plane polarizedlight, and the phenomenon is independentof aniy hypothesis, electromagnetic or other-wise, as to the manner in which the twistingis' produced.
2. The equations given by ProfessorRowland to express the propagation oftwisted plane polarized light are not suit-able for that purpose, for they in fact ex-press the propagation of a uniformly andcontinuously rotated plane polarized ray,
such as is at present unknown to experi-mental physics.
3. The velocity of a twisted plane polar-ized ray is so related to the velocities ofthe right and left circularly polarized rays-of which it is composed that its reciprocalis the arithmetical means of the reciprocalsof its components; and the velocity of Pro-fessor Rowland's rotating pla.ne ray is thearithmetical mean of the velocities of itsright and left circularly polarized com-ponents.
4. The differential equation based on twodifferent electromagnetic hypotheses as tothe action of the medium in producingrotation or twisting of plane polarized light-in a magnetic field involves an equationexpressing the relation of the veloeity ofthis kind of light at zero field to its velocityin the given field. On the hypothesis of or-bital motions of charged ions the differ-ential equations show that the field wouldcause a decrea.se in the velocity of planepolaiized light during the twisting; whileon the hypothesis of charged ions having amotion of translation across the field, thedifferential equations, show that the fieldwould cause a.n increase in the velocity byan amount one-third as great as the de-crease just mentioned. This: increase ordecrease is of the second order of smallquantities, and is so minute as to be atpresent beyond the range of observation,varying as it does as t.he square of theobserved change produced by the field inthe velocity of circularly polarized rays.
5. MacCulloch's differential equationsinvolve practically the same decrease of'velocity by the medium as those based onorbital motions of charged ions.
6. A moderate amount of absorption inthe medium would not practically modifythe conclusions true for perfectly trans-parent media on either hypothesis.
On the Theory of Experiments to DetectAberration of the Second Degree. ED-WARD W. MORLEY. Western Reserve Uni-versity, and DAYTON C. MILLER, CaseSchool of Applied Science. (To be pub-lished in the Proceedings of the Amer-ican Academy of Science, and in thePhilosophical Magazine.)In this paper there is a reconsideration
of the simple theory of aberration of thesecond degree as given by Michelson andMorley in 1887, and of the general theoryas given by Hicks. The effects due to aber-ration of the first, second and higher de-grees have been computed, and the resultsare shown in curves. The conclusion isthat the original theory was correct andsufficient, and that the modifications pro-posed by Hicks are effective in aberrationof the third or fourth degree only, or are(in two instances.) due to errors in histheory.
Report of an Experiment to Detect Changeof Dimenssion of Matter Produced by itsDrift through the Ether. EDWARD W.MIORLEY and DAYTON C. MILLER. (Tobe published in the Proceedings of theAmerican Academy of Science, and inthe Philosophical Magazine.)The paper describes a large interferom-
eter designed for the measurement of etherdrift, and for the determination of anydifferential change in the dimension ofmatter, resulting from such a drift. Thesupport, of the optical parts is a steel truss-pattern cross, which is circumscribed bya square with diagonals fourteen feet long.By repeated reflections the optical path ofthe light is lengthened to two hundred andeleven feet. The whole interferometer isfloated on mercury to render observationspossible in all azimuths. The distancesapart of the mirrors are determined by in-terchangeable rods, which may be of anysuitable material. Experiments have been
made using pine distance pieces, which giveresults in accordance with those of theoriginal experiment made by MNichelsonand Morley in 1887 in which the distanceswere determined by sandstone.The theory given in the precedinog paper
indicates a displacement of the interferencefringes due to ether drift amounting to1.53 wave-lengths, as the apparatus isrotated. The observations from 260 rota-tions show that the displacement is lessthan 0.015 wave-length. As the latterquantity is as small as the errors of obser-vation, the conclusion is that there is nodrift of the ether at the place where theinterferometer is mounted.
Recent Experiments and Theories on- theEther Drift. D. B. BRACE, Universityof Nebraska.
The Elirnination of Gas Action ini Experi-ments on Light Pressure. G. F. HULL,Dartmouth College. (To be publishedin the Philosophical Magazine and in thePhysical Review.)When light is thrown on one vane of a
torsion system suspended in a partialvacuum, the 'Crookes effect' or gas action iselininated, leaving only light pressureeffective, in the following ways: (1) Bymaking the vane accurately vertical; (2)by enclosing the absorbing or reflecting sur-face; (3) by making the vane a cylindricalsurface having its axis coincident with thesuspending fiber; (4) by using inclinedsurfaces and polarized light.Experiments are described and data
given showing that the gas action is elimi-nated through large ranges of air pressurevarying from about half an atmosphere upto a few millimeters of mercury.A simple lecture room experiment is de-
scribed for demonstrating that light pres-sure on a reflecting surface is greater thanthat on an absorbing surface in the ratio
of 1 + r, 1 + r2, where r1 and r2 are thereflection coefficients of the two surfaces.
The Distributiont of Energy in the VisibleSpectrum. EDWARD L. NICHOLS, Cor-nell University. (To be published in thePhysical Review.)This paper gives definite numerical. and
graphical da.ta for the variation of in-tensity with wave-length in the visiblespectrum of various sourees of light suchas the Hefner lamp, the ordinary gas flame,the petroleum flame, the acetylene flame,the Nernst filament, the lime light, themagnesium light and the carbon arc light;also in the spectrum of incandescent bodiessuch as carbon, platinum and zinc oxide atknown temperatures.
Hitherto our knowledge of these spectrahas been relative, each being compared withsome other takein as a reference standard.It is now possible, however, to reduce allspectrophotometric comparisons to absolutemeasure.
A Note on Interference vith the Bi-Prism.WM. MCCLELLAN, University of Penn-sylvania.The condition that diffraction and inter-
ference lines obtained by me.ans of the bi-prism shall be seen separately, depends onthe relative positions of the screen prismand slit, and the angle of the prism. Thewriter has taken several photographs toillustrate the variou's fields which may beobtained from the same prism.
fI'he Evolution of lydrogen from theCathode in Gases and its Association withCath ode Rays. CLARENCE A. SKINNER,University of Nebraska.
Exhibit of Liquid Air Machine in Opera-tion. ARTHUR W. GOODSPEED, Univer-sity of Pennsylvaniia.
DAYTON C. MILLER,Secretary of Section B.
THE CONVENTION OF THE ASSOCIATION OFAMERICAN AGRICULTURAL COLLEGES
AND EXPERIMENT STATIONS.
TIHE eighteenth annual convention ofthis association was held in the ChamberlainHotel, at Des Moines, Iowa, November 1-3.It was the first meetingf under the new con-stitution, which reduces the number of sec-tions from five to two; and the advantageof the new plan was very marked in en-abling delegates to follow the discussionsmore closely, and iln concentrating the delib-erations upon quest-ions of administrationand methods of work. The two sectionsunder the present constitution are (1) oncollege work and administration, and (2)experiment station work.The general sessions were presided over
by Dr. W. 0. Thompson, of the Universityof Ohio, who delivered the customary presi-dential address. This dealt with 'SomeProblems in the Colleges of Agricultureand Mechanic Arts,' and gave specialattenition to the agricultural phase of theirwork. Among the problems noted were theconditions in the agricultural communities,the much-discussed tendency away from thefarm, and the frequent lack of opportunityon the part of the farmer's boy for indi-vidual initiative. It was urged that farmlife must not be the refuge of necessity,that not all farmers' sons are suited to befarmners any more than all lawyers' sonsare suited to that profession, and thatmarked changes in farming have takenplace in recent years which call for specialaptitude and training quite as much as anyother work in life. It was pointed out thatintelligent operation of the farm is nownecessary for any mrargin of profit, and thefallacy that unintelligent men can makesuccessful farmers or satisfactory farmlaborers was denounced. 'We need toknow that intelligence on the farm willproduce results just as surely as elsewhere,'
