4i6 



NATURE 



[May 25, 191 1 



Law of Motion. — Acc«icrution» occur only in oppoitite 

 pair*, the ratios of which an- constant for given particles. 



Definition of Mass. — 'i'he niaisc!> of particlcb are positive 

 constants, inversely as their iiiutuul accelerations. 



Definition of Force. — Force is the product, mass into 

 acceleration, and has the direction of the acceleration. 



Choice of Axes. — Since motion is relative, force and 

 mechanics are relative also. Hence, the foregoing and any 

 problems based upon them should be referred to axes 

 which, in each case, yield a mechanics most appropriate 

 to the phenonn-na und»»r discussion. 



\<iitini,'h;iin, M.iv 12. E. If. R^RTON. 



I AM iiiucii obliged to the Editor of .Natikk for giving 

 me an opportunity of commenting upon Prof. Barton's 

 letter. In the second edition of my book on " Theoretical 

 Mechanics " 1 have expressed my ideas on the subject at 

 such length that it is unnecessary to go into details here. 

 It may suflice to say that the first two of Prof. Barton's 

 proposed enunciations seem to me to be too abbreviated 

 to be of much value. To anyone who understands the 

 theor)' of mechanics, as explained by the writers whom he 

 cites, such statements could be of little use, while to any- 

 one who does not they might be misleading. The third 

 enunciation does not distinguish between force and the 

 quantity which Routh called " effective force " and I call 

 "kinetic reaction." The distinction appears to me to be 

 important. The fourth enunciation would seem to permit 

 an undesirable degree of freedom in respect to the choice 

 of a reference system. I do not wish to suggest that Prof. 

 Barton means by his brief enunciations something different 

 from what I mean In my book, but rather to point out 

 that such lM-vit\ as he aims at may be inconsistent with 

 clearness in ili. statement of principles. One way of 

 bringing the results of modern critical discussions concern- 

 ing the laws of motion within the reach of the " ordinary 

 student " would be to publish a short tract, on the same 

 scale, say, as Maxwell's " Matter and Motion." In such 

 a tract summary enunciations could be accompanied by 

 adequate explanations. Would not this be better than 

 providing teachers with a set of enunciations? 



May 18. A. E. H. Love. 



Further Experiments with the Gramophone. 



I HAVE just seen Prof. McKendrick's letter in your 

 issue of April 20, describing the experiments he has made 

 with a view to improving the quality of the notes repro- 

 duced by a gramophone. 



Some five or six years ago, when I was working at 

 the auxetophone, I tried a number of similar devices, and, 

 to a very large extent, succeeded in getting rid of the 

 objectionable hissing and scratching sounds. 



One of the horns I tried consisted of a wooden tube 

 of rectangular section and gradually increasing area, which 

 was doubled backwards and forwards on itself in the shape 

 of a flat zigzag, and was practically identical with the 

 metal horn illustrated in your paper. 



In the end I found it was best to use a coiled metal 

 trumpet of large size and gradually increasing area and 

 about 48 feet long, in which I introduced several right- 

 angled and " U " shaped bends ; further, I fitted a " T " 

 shaped tube close to the reproducer, which made a con- 

 siderable improvement in the quality of the tone. The 

 longer sound waves passed through this " T " shaped bend 

 with little loss, but the very short waves, which caused 

 most of the scratching, were absorbed at the bend, espe- 

 cially if the blank end of the " T " was filled with cotton 

 wool or some other similar substance, or if an inner 

 sliding tube, with the end closed, was introduced into the 

 blank end of the "T," and pushed in, so as to throttle 

 the sounds at the bend. 



I also fitted a flexible joint between the needle and the 

 actual reproducer, which further eliminated these high- 

 period vibrations. This flexibility was obtained bv giving 

 the joint very large clearance, and filling the space in 

 between with a highly viscous substance. 



I found considerable improvement, as well, in the tone 

 when a paper diaphragm, or when moderate quantities of 

 paper, linen, &c., were put in the trumpet. 



NO. 2169, VOL. 86] 



In conclufion, 1 might uzy that my own ' 

 quite bear our Prof. McKendrick's opinion on 

 ante of usinf; ttuitably !ihap4-d trumpets in order to 

 pleasaiu natural reproductions of musical tone* and 

 human voice. CHARi.r<- ^ " ■• 



Heaton Works, Newcastle^n-Tyne, Ma> 



German Ea«t African Dinosaurs. 



With reference to your note on the German En'. 

 African Dinosaurs (Natuke, -May 18, p. 390), / ' 

 of May reproduces an interesting series of 1 

 of the remains, taken on the site of the excavatiwis. 



.Matlock, May 20. F. Gillman. 



BREATH FIGURES. 



THE manner in which aqueous vapciur cond'-"-- 

 upon ordinarily clean surfaces of glass orni 

 familiar to all. Examination with a magnifier sl.„.. 

 that the condensed water is in the fonn of small lenses, 

 often in pretty close juxtaposition. The number and 

 thickness of these lenses depends upon the cleanness 

 of the glass and the amount of water deposited. In 

 the days of wet collodion ever)- photographer j; 

 of the success of the cleaning process by the unifoi 

 of the dew deposited from the breath. 



Information as to the character of the deposit is 

 obtained by looking through it at a candle or small 

 gas flame. The diameter of the halo measures the 

 angle at which the drops meet the glass, an angle 

 which diminishes as the dew evaporates. That the 

 flame is seen at all in good definition is a proof that 

 some of the glass is uncovered. Even when both 

 sides of a plate are dewed the flame is still seen 

 distinctly though with much diminished intensity. 



The process of formation may be followed to some 

 extent under the microscope, the breath being led 

 through a tube. The first deposit occurs very suddenly. 

 As the condensation progresses, the drops grow, and 

 many of the smaller ones coalesce. During evapora- 

 tion there are two sorts of behaviour. Sometimes the 

 boundaries of the drops contract, leaving the gla>s 

 bare. In other cases the boundary' of a drop remains 

 fixed, while the thickness of the lens diminishes until 

 all that remains is a thin lamina. Several successive 

 formations of dew will often take place in what seems 

 to be precisely the same pattern, showing that the 

 local conditions which determine the situation of the 

 drops have a certain degree of permanence. 



An interesting and easy experiment has been de- 

 scribed by Aitken (Proc. Ed. Soc. p. ()4, 1893). Clean 

 a glass piate in the usual way umil the breath depjosits 

 equally. 



"If we now pass over this clean surface the point of a 

 blow-pipe flame, using a very small jet, and passing it 

 over the glass with sufficient quickness to prevent the 

 sudden heating breaking it ; and if we now breathe on 

 the glass after it is cold, we shall find the track of the 

 flame clearly marked. While most of the surface looks 

 white by the light reflected from the deposited moisture, 

 the track of the flame is quite black : not a ray of light 

 is scattered by it. It looks as if there were no moisture 

 condensed on that part of the plate, as it seems un- 

 changed ; but if it be closely examined by a lens, it will 

 be seen to be quite wet. But the water is so evenly dis- 

 tributed, that it forms a thin film, in which, with proper 

 lighting and the aid of a lens, a display of interference 

 colours may be seen as the film dries and thins away." 



" Another way of studying the change produced on the 

 surface of the glass by the action of the flame is to take 

 the [plate], as above described, after a line has been drawn 

 over it with the blow-pipe jet, and when cold let a drop 



