ISO 



SCIENCE. 



[Vol. XXI. No. 52S 



to a place among carbohydrates as derivatives or modiScations of 

 the same. 



E. Fischer proposes to apply the name "sugars" to all the 

 members of this homologous series, to which he has lately added 

 the glycol-aldehyde CaH402 as the simplest possible example. 

 The popular conception of the properties of a sugar are not, bow- 

 ever, easily reconciled with the properties of some of these bodies, 

 while "carbohydrates'' at least possess some reference to their 

 impirical composition. With regard to gljcol-aldehyrle. more- 

 over, its optical inactivity would exclude it from the list under the 

 conditions here proposed, although its constitution undoubtedly 

 satisfies the requirements. 



ELECTRICAL NOTES. 



Variations in Resistance. 



In a recent article in the Philosophical Magazine appears a paper 

 by .Mr. Fernando Sandford, entitled " A Necessary Modification of 

 Ohm's Law." Why it should have been given this title does not 

 appear, for it nowhere calls in question the law which goes by 

 Ohm's name. A better title would have been •' On the Variation 

 of Resistance of a Conductor with Change of the Medium Sur- 

 rounding It." The facts observed are of interest, though not 

 new, as it has long been known that the resistance of a wire 

 changes when immersed in different gases. Chatelier, for exam- 

 ple, found that the resistance of a silver wire changed enormously 

 when immersed in hydrogen gas. and that if left in it for some 

 time its temperature coefficient changed also. Mr. Sanford has 

 extended the list considerably, his experiments, though made with 

 a wire of one metal only, i.e., copper, embrace a great variety of 

 mediums, both liquid and gaseous. That the variation is due to 

 the causes noticed in the experiments of M. Chatelier and not 

 to heating of the conductor, as proposed by some, is probable 

 from the following considerations. The total heat generated in 

 the wire, using the ordinary coefficients of emissivity for polished 

 copper, would not raise the temperature of the wire more than 

 the one ten-thousandth of one degree centigrade, and the increase 

 of resistance from this cause would be inappreciable. But the 

 effect of a thin film on the wire would be far different. It was 

 first pointed out by Mr. Kennelly to the writer that the extremely 

 thin iilm of tin on electric conductors was sufficient to lower the 

 resistance of moderately small wires as much as five percent. If 

 we suppose that when a wire is placed in a gas like SOo a thin 

 film of a compound of the copper and the gas is formed, only the 

 one twenty-five-thousandth of an inch in thickness, it will ac- 

 count for all the phenomena observed by Mr. Sanford. For, as 

 the wire experimented on was one millimetre in diameter, the 

 formation of a layer ^5-5^^ of an inch thick would reduce the cross 

 section of the copper by two-tenths of 1 per cent, and therefore 

 increase the resistance by 0.2 per cent, or nearly the maximum 

 change observed by Mr. Sanford. This thickness of film is not 

 much greater than the thickness of the films which cause the 

 iridescent colors on steel, being about three to live times as thick; 

 so that we see that the slightest action of ihe gases on the surface 

 of a wire would change the resistance quite appreciably, and on 

 exposure to air the wire would recover itself again. It should 

 be added, moreover, that such films would not necessarily be 

 visible. 



An easy way of settling the question would be to use wires of 

 different diameters. With a wire whose diameter was .0035, or 

 No. 40 B. W.G. , and which is furnished for commercial purposes, 

 the resistance should vary as much as one and a half per cent, 

 while with a wire one centimetre in diameter it should be inap- 

 preciable. R. A. F. 



A JOINT meeting of the Scientific Alliance of New York, in 

 memory of Professor John Strong Newberry, will be held at 

 Columbia College, Monday evening, March 37, 1893, at 8 o'clock. 

 An address will be given by Professor H. L. Fairchild, "A Memoir 

 of Professor John Strong Newberry." Remarks will be made by 

 others, and a number of letters regarding Professor Newberry 

 will be read. 



LETTERS TO THE EDITOR. 



♦ ** ijorrespondents are requested to be as brief as possible. The vyriter's name 

 is in all cases required as proof of good faith. 



On request in advance, one hundred copies of the number containing his 

 communication will ne furnished free to any correspondent. 



The editor willbe glad to publish any queries consonant with the character 

 of the journal. 



Does the Ether Absorb Light ? 



Whether or not lisht is absorbed in any degree by the ether 

 through which it passes has been argued a good many times, and 

 to-day is not settled on any experimental basis. That it is not so 

 absorbed to any considerable degree is evident from the light 

 from such distant stars that reaches us. From theoretical con- 

 sideraiions some have concluded that many more stars would 

 probably be seen by us if in some way their light was not stopped 

 by the ether, and that the midnight sky would or should lie 

 brighter than it really is. 



In all the treatments of the subject which I happen to have 

 seen, there is one important element which has not been consid- 

 ered at all, and to me it seems as if that one would account for 

 the limit to the number of stars we see without assuming that 

 the ether possesses the ability to transform energy within itself, 

 which would be the case if the energy of waves like light waves 

 were changed into any other kind of eneigy not capable of af- 

 fecting our eyes This fact is, that, in order to see, some energy 

 is needful. I mean that there must be some limit to the ampli- 

 tude of the vibratory movement beyond which we could not see, 

 simply because the energy of the wave is insufficient; so that no 

 matter what the intrinsic brightne.=s of a given light may be, if it 

 be far enough removed from an observer it will cease to be visi- 

 ble, simply because the energy of the waves is too small to excite 

 the sensation. As the energy of such radiant energy on unit area 

 varies inversely as thesquare of the distance, and as the amplitude 

 of the vibrations at the initiating atoms or molecules can at best 

 not exceed the diameter of tlie atoms or molecules, the extreme 

 minuteness of the amplitude at the distance of the fixed stars 

 from us shows how exceedingly delicate is the eye for perceiving 

 it at all. The enormous frequency of the waves gives them a 

 degree of energy they could not otherwise have; but if there 

 were no amplitude there would be no energy, and it is to be con- 

 ceived that if space be illimitable and the number of stars be in- 

 finite, yet with eyes constituted like ours only the light of stars 

 within a limited space would be visible, and such optical data 

 would give no reason for holding that what could be seen was 

 the whole, nor for the conclusion that the light from more dis- 

 tant stars was absorbed by the medium through which it was dis- 

 tributed. 



The photographic work done in this field testifies to the same 

 conclusion when we are presented with the image of a star whieh 

 had never been seen. The photographic plate acts cumulatively 

 and if one minute's exposure is not enough, take ten minutes or 

 ten hours, but the eye cannot so act; if one cannot see an object 

 in a second hecan see it no better by continued looking. Icon- 

 elude, therefore, that we have no evidence that the ether absorbs 

 any of the energy of the ether waves. A. E. D01.BEAR. 



Tuft'3 College, Meias., Maroh 9. 



Natural Selection at Fault. 



In your issue of Feb. 17, Mr. Richard Lees replies to the rather 

 misleading article of Mr. J. W. Slater in your issue of Jan. 20, 

 and takes, it appears to me, the right view of the case as regards 

 the Felid», but misses it when be attempts to account for the 

 hen's cackle. No one reason will account for the latter. Fre- 

 quently the hen that is a member of a large barn-yard flock may 

 be observed cackling at the top of her voice prior to the laying of 

 the egg, and it has been my observation that in 9 cases out of 10 

 this is due to the fact that she has found a usurper in her nest in 

 the person of another hen engaged in egg laying. Close observa- 

 tion, covering many years, leads me to think that the cackling 

 after the egg is laid has nothing whatever to do with nest-dis- 

 closure or nest hiding, but is simply a notification to the cock of 

 the flock that the important task of the day is accomplished. 



