38 



NATURE 



\]\Tav 9, 187: 



of a lieavenly body Ijy variations in the refrangibility of tlie 

 rays which it emits — motions often impossiMc even to detect 

 by any other means. I therefore deem it proper that I should 

 proceed to state the delicate conditions on which depend the 

 perfection of experiments which so satisfactorily elucidate the 

 nature of those grand and refined problems offered to spectral 

 observation. 



It is, first of all, essential that forks i and 2 should really be 

 in unison. Two forks, sounded together, may give no percep- 

 tible beats, for they may constrain each other into a common 

 forced oscillation, and thus both will give the same number of 

 vibrations, yet may be removed from equality when separ.itely 

 vibrated. The process I have adopted is as follows ; Three 

 forks are taken which are supposed to give the same number of 

 vibrations in a given time. They are supported on india-rubber 

 tubing, and are thus insulated. One of the forks is now loaded 

 so that it gives two or three beats in a second, with one of the 

 other two that are to be brought into exact unison. The interval 

 of time occupied by twenty or thirty of these beats is accurately 

 determined by means of a chronograph (one of Casella's regis- 

 tering stop-watches dots very well). The interval occupied by 

 the same number of beats given with the second fork is now 

 ascertained, and if it differs from that given by the first, the 

 quicker vibrating fork is made to give the same number of beais 

 as the slower by loading it with wax. When the forks have 

 thus been carefully adjusted, I have had no difficulty in pro- 

 jecting the ball, in Exp. i, at a distance of sixty feet, and I 

 believe that it could have been accomplished at a distance of 

 100 feet. The ball of cork should be spha-ical, so that it will 

 always just touch the fork, no matter how much it may rotate 

 around its susj^ending thread, which latter should consist of only 

 one or two fibres of unspun silk. The cork is rendered as 

 smooth as possible and is then %'arinshcd ; this is important, for 

 the varnish gives a firm coating to the bdl, without sensibly in- 

 creasing its weight, and is especially useful in covering the minute 

 asperities or elastic projections on its surface, which otherwise 

 would act as "buffers" to the impacts of the fork and deaden 

 its projectile effects. 



The above-stated conditions having been obtained, no phy- 

 sicist will have any difficulty in repeating these experiments. 



A machine has been devised by which a uniform motion of 

 tr.'.nslation can be given to the forks, and with this I propose 

 making a quantitative investigation of the phenomena, using an 

 apparatus essentially the same in its action as the one here 

 described. 



We may substitute for the suspended cork-ball a light plane 

 n.irror, held between two stretched vertical fibres, while one of 

 its edges touches the fork. The motions of a beam of light 

 reflected from the mirror to a screen, indicate most beautifully 

 the vibrations of the fork. This ingenious and most delicate 

 device for detecting vibrations is due to Prof. O. N. Rood, of 

 Columbia College, N.Y., who first used it in a public lecture, 

 delivered in New York on the 28th of last December. We have, 

 however, in our special work, found the image of the projected 

 ball more convenient, and sufficiently delicate, for our experi- 

 ments. 



Quantitalivc yelntions in the c.\pcyimciils and andhtgu-iil fads in 

 the phenomena of light. 



The UT3, No. I fork, makes 256 complete vibrations in one 

 second, while fork No. 3 makes 254, giving for the respective 

 wave-lengths of these vibrations 4 '367 and 4'40i feet, which we 

 will designate in order as X and \'. We will take 1,118 feet per 

 second as the velocity of sound at 5o° F. 



N0W256 vibrations in 1,118 ft. make A = 4-367 ft. 



and 254 „ „ 1,118 - 2A.( = i,t09'266)giveA = 4,357 ft. 



As the velocity of propagation of the vibrations and X are the 

 same in both cases, it follows that ( " = - )■ the number of vibra- 

 tions in a second, reaching a distant point, is the same, and, 

 therefore, 256 vibrations from a body at rest will produce the 

 same effect on a distant surface, as 254 vibrations emanating 

 from a body which moves toward that surface, with a velocity of 

 2 \, or of 8734 feet per second ; and this is the velocity we gave 

 the fork in Exps. 6 to 9. 



We will now examine the analogical phenomena in the case of 

 light. Let fork No. I, giving 25G vibrations a second, stand for 

 595 millions of millions vibrations a second, which we will take 



as the number of vibrations made by the ray D[ of the spectrum. 

 Then fork No. 3 will represent 590 millions of millions vibra- 

 tions per second, which gave a wave-length '0000042 millimetre 

 longer than that of D,, and nearly corresponds with an iron line 

 situate '4.2 div. below Dj on Angstrom's chart. We saw that fork 

 No. 3, giving 254 vibrations a second, had to move toward the 

 ear with a velocity of 873 (.ft , to give the note produced by 256 

 vibrations per second, emanating from a fixed point ; .so a star 

 sending forth the ray which vibrates 590 millions of millions times 

 a second, will have to move toward the eye with a velocity of 

 28,470 miles per second to give the colour produced when ray 

 Dj emanates from a stationary flame. 



SCIENTIFIC SERIALS 



Aniialen </,-i- Chcinie mid Phannacie, October 1S71. Naumann 

 has made a long series of experiments on the dissociation-tensions 



01 am.monic carbonate, he finds that when it is volatilised it is 

 entirely decomposed into ammonia and carbonic anhydride, and 

 that for lower temperatures the dissociation-tensions of this body 

 increase by increase of temperature precisely as the tensions of 

 other substances. Leist has obtained three compounds of 

 bismuth oxide with sulphuric acid, all of which are basic salts, 

 he has not been able to form the normal salt except in combina- 

 tion with potassium. Faust has made a series of experiments on 

 the derivatives of phthalic acid, he has obtained nitrophthalic, 

 bromophthalic, and dechlorophthalic acids. Faust and Saame 

 hive nrade a careful examination of the chloro-compounds, both 

 addition and substitution of naphthaline : this work has already 

 b?en performed many years ago by Laurent ; the authors have 

 thought fit to commence a revision of the subject, but it is as yet 

 far from complete. A very long paper by Schutzenberger follows 

 "on the acetyl derivations of carbo-hydrates, mannite and its 

 isomerides, and on certain vegetable products," this contains some 

 interesting though complicated results. A translation of Dr. 

 Mills' paper on the nitration of chloroform, and two other 

 papers of less interest complete this number. 



Annalcs de Chimie d dc Pliysiqnc, March 1872. — The greater 

 portion of this number is occupied by the second part of MM. 

 Piene and Puchot's researches on some of the bodies produced 

 in fermentation. They give the results of a very detailed study 

 of propylic alcohol, its haloid ethers, the formiate, acet.ate, pro- 

 pionate, butyrate, and valerate, and propylic aldehyde ; butylic 

 alcohol and the same series of ethers as above, and amylic alcohol 

 with its butyrate and valerate. Besides these we have the de- 

 tailed description of sever.al other ethers, methyl valerate, and 

 ethyl propionate and valerate, forming altogether a very com- 

 plete and exhaustive monograph on these subjects. The author 

 has also made some interesting observations on the "simul- 

 taneous distillation of water with certain alcohols insoluble 

 therein." Thus a mixture of water and amylic alcohol, when 

 submitted to distillation, boils at 96°, and a definite proportion 

 of the two bodies is found in the distillate, at this temperature 



2 parts of water and 3 of amylic alcohol invariably condense ; 

 should the water be in excess the whole of tl-.e amylic alcohol 

 will pass over, the thermometer remaining at 96'. Butylic alcohol 

 and water distil over at 90'5' when a constant mixture of 5 parts 

 of alcohol and I part of water condenses. — M. Bourgoin has 

 electrolysed a solution of potassic phthalate, and finds that it 

 splits up into water, carbonic oxide, and carbonic anhydride, an 

 aqueous solution of phthalic acid does not appear to be decom- 

 posed by the electric current. 



The Scottish Naturalist for April contains a number of short 

 articles on various branches of -Scottish Natural History. Among 

 the more interesting may be mentioned especially a note by Dr. 

 Buchanan White on the discovery in Braemar of a colony of 

 Zyg<rna e.\n/ans, a common moth in the Alpine districts of 

 Southern Europe and in Scandinavia, but hitherto unknown in 

 Britain. Dr. White considers it, like some of the characteristic 

 plants of the district, a relic of the glacial epoch which once 

 overspread Scotland ; its characters are intermediate between 

 the northern .and southern forms. — Mr. George Sim contributes 

 an important p.aper, comprising a list of the stalk-eyed Crustacea 

 of the north-cast coast of Scotland, with descriptions of new 

 genera and species, and a plate. — The instalment of the cata- 

 logues of Insecta Scotica includes a continuation of the Lepidop- 

 tera by Dr. Buchanan White, and the commencement of the 

 Coleoptera by Dr. D. Sharp. 



