Jan. 22, 1885] 



NA TURE 



269 



So we learn that the things in a room warmed by 

 radiation (sunlight or open fire), because they are warmer 

 than the air of the room, do not tend to get very dusty. 

 But in a room warmed by hot piping or stoves, things 

 are liable to get very dusty because the air is warmer than 

 they are. 



Finally, let us turn to electrical phenomena in dusty air. 

 Just as a magnet polarises iron tilings, and makes them 

 attract each other and point out the lines of force, so an 

 electrified body polarises dust particles, and makes them 

 point out the lines of electrostatic force. It is therefore 

 very interesting to watch electrical phenomena in illumi- 

 nated smoky air. 



The pyroelectric behaviour of tourmaline for instance is 

 beautifully shown by the aggregation of dust in little 

 bushes at the opposite poles of the crystal. Mica often 

 exhibits strong electrical actions. But perhaps the most 

 curious thing of all is what happens when a brush dis- 

 charge begins in such air. The violent and tumultuous 

 action must be witnessed — it can hardly be described ; 

 but it does not last long, for in a few seconds every 

 particle of dust has disappeared, condensed on the walls 

 and floor of the vessel. 



[An experiment of discharging from a point connected 

 with one pole of a Yoss machine into a bell-jar of illumi- 

 nated magnesium smoke was then shown. It is a very 

 easy experiment, and rather a striking one. A potential 

 able to give quarter-inch or even one-tenth-inch spark is 

 ample, and better than a higher one. The smoke par- 

 ticles very quickly aggregate into long filaments which 

 point along the lines of force, and which drop by their 

 own weight when the electrification is removed. A 

 higher potential tears them asunder and drives them 

 against the sides of the jar. A knob polarises the particles 

 as well as a point, but does not clear the air of them so 

 soon. If the bell-jar be filled with steam, electrification 

 rapidly aggregates the globules into Scotch mist and fine 

 rain. 1 ] 



This experiment shows how quickly air may be cleared 

 of its solid constituents by a continuous electrical discharge. 

 The fact may perhaps admit of practical application 

 in clearing smoke-rooms, or disinfecting hospital air. It 

 also must have a close bearing on the way in which 

 " thunder clears the air,'' on thunder-showers, and perhaps 

 on rain in general. Sir Wm. Thomson's " effect of curva- 

 ture on vapour-tension" shows that large cloud globules 

 increase at the expense of small ones, and so may 

 gradually grow into raindrops ; but under electrical influ- 

 ence rapid aggregation of drops mu-t occur. The large 

 drops so formed may be upheld by the electrical attraction 

 of a strongly charged thunder-cloud, but as soon as the flash 

 occurs, down they must come. Lord Rayleigh made 

 some interesting observations on the effect of a feeble 

 electrical charge in inducing a spreading water-jet to 

 gather itself together {Proc. Roy. Soc, No. 221, 1882) ; and 

 Prof. T.iit 1) is pointed out in his lecture on Thunder- 

 storms (NATURE, vol. xxii. pp. 339, 436) that aggregation of 

 feebly charged drops into larger ones is of itself sufficient 

 to raise their potential. One strongly charged cloud 

 would thus act on another, aggregating its drops, and so 

 raising its potential until a flash is a necessity. 2 



It seems not impossible that some use may be made of 

 this aggregating power of electricity on small bodies, such 

 as smoke particles and mist globules. In coming in this 

 country welayfi ir some hours outside the Straits of Belle Isle 

 in the midst of icebergs mingled with fog. Icebergs alone 

 are not dangerous but beautiful. Fog is an unmitigated 



1 I find that unless one claims a lecture experiment it 1- i immonly treated 



echauffic. It is pardonable, therefore, and indeed only '!"- to Mr. 



Clark, who has been associated with me in the dust research, to state that 



il rval -us are original. A small cellar can be cleared of thick 



turpentine smoke pretty quickly by a point discharge. 



11 1I1 initial potentialof the second cloud were opposite to that of the first, 



I pass between the two clouds : if it were similar, its risi uld 



11: the potential of the first cloud, and so cause it to spark into something 



nuisance. Electric light is powerless to penetrate it ; and 

 it was impossible, as we lay there idle, not to be struck with 

 the advisability of dissipating it. It is rash to predict what 

 can be done, it is still rasher to predict what can not. I 

 would merely point out that on board a steamer are donkey- 

 engines, and that these engines can drive a very powerful 

 Holtz or Wimshurst machine, one pole of which may be 

 led to points on the masts. When electricity is discharged 

 into fog on a small scale, it coagulates into globules and 

 falls as rain — perhaps it will on a large scale too. Oil 

 stills the ripples of a pond, and it has an effect on ocean 

 billows ; just so an electric discharge, which certainly 

 coagulates and precipitates smoke or steam in a bell-jar, 

 may possibly have an effect on an Atlantic fog. I am 

 not too sanguine, but it would not cost much to try, and even 

 if it only kept a fairly clear space near the ship, it 

 would be useful. There are other possible applications 

 of this electrical clearing or deposition of dust, but I am 

 not here to talk of practical applications but of science 

 itself. A homely proverb may be paraphrased into a 

 useful motto for young investigators. Stick to the pure 

 science and the applications will take care of themselves. 

 I am not one to decry the applications of science for the 

 benefit of mankind, far from it, but while the rewards of 

 industrial applications are obvious and material, and such 

 as will always secure an adequate following, the rewards 

 of the pursuit of science for its own sake are transcen- 

 dental and immaterial, and not to be imagined except by 

 the few called to the work. That call entails labour and 

 self-sacrifice beyond most other, but they who receive it 

 will neglect it at their peril. 



HEREDITARY DEAFNESS" 

 'THE startling title of Mr. Graham Bell's admirable 

 •*• memoir is fully justified by its contents. It appears 

 that there are upwards of 33,000 deaf mutes in America, 

 mostly collected in large institutions forming social worlds 

 of their own, whose inmates intermarry or else contract 

 marriages with the hearing relatives of their fellow pupils, 

 who themselves, in many cases, must have an hereditary 

 though latent tendency to deafness. This state of things 

 has been going on increasingly for two or more genera- 

 tions, with the result that congenital deafness, which in 

 other countries appears sporadically, and mostly fails to 

 obtain an hereditary footing, has become artificially pre- 

 served in America, and is intensified by inter-marriages, 

 until a deaf variety of the human race may be said to be 

 established. There can be no question, after reading the 

 mass of evidence submitted by Mr. Graham Bell, of the 

 general truth of this summary statement. That precise 

 knowledge that we should be glad to possess, of the 

 strength and peculiarity of the hereditary taint, is unfor- 

 tunately unattainable owing to the imperfection of the 

 records kept at the institutions of the after history of 

 their pupils ; but the data, such as they are, have been 

 handled with great statistical skill by the author, so that 

 he has squeezed all the information out of them that they 

 appear competent to give. 



\\ <■ ma)- now go a little more into details. It appears 

 that (put of six asylums, with an aggregate of 5823 pupils, 

 295 per cent, have deaf relatives. Also that nearly half 

 the pupils contract marriages, and that 80 per cent, of 

 those who do so, marry together. This ratio of inter- 

 marriage is much greater than it was at the beginning of 

 the century, and it appears to have steadily increased 

 from then up to the present time It is unfortunate that 

 the imperfection of the records kept at the institutions 

 make it difficult to ascertain the exact rate of the increase 

 or the precise fate of the issue of all the marriages. This 

 latter fact may, however, be estimated by working back- 



1 "Upon the Formation of a Deaf Variety of the H 

 ander Graham Bell, National Academy of S'~' 

 November 13, 1883. 



jman Race," by Alex- 

 New Haven, U.S.A., 



