206 



NATURE 



\yan. 14, 1875 



in a quiescent part of that fluid with the velocity in ques- 

 tion, would run through a space equal to ten thousand 

 times the length of its diameter in one second, and con- 

 sequently would come into contact with at least sir hun- 

 dred thousand ^\^(^x<trA particles of water in that time. 



" Hence it appears how inconceivably short the time 

 must be that an individual particle, in motion, of any 

 fluid can remain in contact with any other individual 

 particle, not in motion, against which it strikes in its pro- 

 gress, however slow that progress may appear to us to be 

 through the quiescent mass of the fluid ! 



" Supposing the contact to last as long as the moving 

 particle employs in passing through a space equal to the 

 length of its diameter — which is evidently all that is 

 possible, and more than is probable— then, in the case 

 just stated, the contact could not last longer than 

 txAt.-« part of a second I This is the time which the 

 cannon bullet, flying with its greatest velocity (that of 

 1,600 ft. per second), would employ in advancing two 

 inches. 



" If the cannon bullet be a nine-pounder, its diameter 

 will be four inches, and if it move with a velocity of 1,600 

 feet in a second, it will pass through a space just equal to 

 4,800 times the length of its diameter in one second. But 

 we have seen that a particle of water moving looth of 

 an inch in a second actually passes through a space 

 equal to 10,000 times the length of its diameter in that 

 time. Hence it appears that the velocity with luhich the 

 moving body quits the space it occupies is more than 

 twice as great in the particle of water as in the cannon 

 bullet ! " 



I am sorry that space does not permit further quotation 

 of this essay, in which the author goes on to show thaj- 

 inequality of fluid temperature is one of the leading phe. 

 nomena of animal life ; that respiration raises the heat in 

 oi'.e part, while insensible perspiration cools another ; 

 that stimulation of all kinds is accompanied with dis- 

 turbance of temperature and the consequent motion of 

 particles, which he i-egards as the life of fluids. 



Of course it is not supposed that Rumford, by these 

 ingenious speculations, supplies any mechanical solution 

 0'.' the mystery of conscious vitality, but his suggestions 

 have the merit of showing that a vast amount of mole- 

 cular activity is a demonstrable result of simple well- 

 known facts. He obtains this activity without invoking 

 the aid of those profound assumptions in which the 

 brilliant iraaginations of modern mathematicians so 

 luxuriously revel when they reason upon the vibrations, 

 gyrations, &c., of the component particles of interatomic 

 atmospheres. 



In spite of all the progress we have made in physical 

 science, these essays, written for the most part during the 

 last century, contain a great deal that is still suggestive 

 and worthy of thoughtful reading both by popular 

 students and experts in physical and social science. 

 This is especially the case in the essay on " The Propaga- 

 tion of Heat in Fluids," reprinted in vol. i. of this work. 

 Many of the conclusions and speculations are now de- 

 monstrably erroneous, but some of the suggestions — more 

 particularly those in chap. iii. on the Chemical Action of 

 Light — are worthy of far more attention and investigation 

 than they have yet received. They are avowedly very 

 bold, but the author tells us frankly that their temerity 

 " has not been entirely without design ; " that " philoso- 

 phers may be enticed and they may be provoked to action," 

 and that he has " endeavoured to use both these methods," 

 even with conscious imprudence, for the purpose of ex- 



citing them to further investigation of the subjects for 

 which he has such " passionate fondness.' 



It will be well if the republication of these essays 

 contribute to the fulfilment of Rumford's enthusiastic 

 wishes. W. Mattieu Williams 



THE SILKWORM COCOON 

 Le Cocon de Sole. Histoire de ses transformations, 

 description dcs races civilisees ct rustiqucs, production 

 et distribution gt'ographiques, maladies des vers a sole, 

 physiologic du cocon ct du fil du sole. Deuxifeme 

 Edition. (Paris : J. Rothschild, 1875.) 



WE have received an advance copy of M. E. 

 Duseigncur-Kldbei-'s monograph, " Le Cocon de 

 Sole," dated for 1875, the get-up of which is calculated at 

 once to arrest attention and excite" interest. The 248 

 quarto pages of clearly printed letterpress containing his 

 information, admirably arranged in methodic form, are 

 accompanied by thirty-seven'plates executed in'photo-typo- 

 graphy, and a map of the world; indicating the localities 

 where silkworms are cultivated. Twenty-eight of the 

 plates are devoted to jhe illustration of the different types 

 of cocoons from different countries, of which as many as 

 195 are figured from "photographs. 



Such a work was, he says, quite impossible twenty 

 years ago, and it is only in consequence of diseases that 

 it is possible now. Each district prided itself on the silk 

 it produced, and did not trouble to know what other 

 countries were doing, until the enfeeblement of some and 

 the destruction of other types by disease compelled 

 growers to seek fresh types from a distance, and thus 

 accumulated the information which M. Duseigneur- 

 Kldber has compiled and presented in this attractive 

 form. Many of the types he thinks will probably not be 

 again met with in cultivation, and it is only through 

 noticing and recording facts as they came under his notice 

 during a series of years that his information has been 

 obtained. Looking to the past, he finds that from 1700 

 the years of disease were 1702, 1720, 1750, 17S7, but the 

 chroniclers give no intimation of the character of the 

 disease. In 1810 the "plague" was described by M. 

 Paroletti. The affected worm exhibited small spots all 

 over its body, which were gangrenous, and appeared to be 

 caused by the same disease now known as " Muscardine." 



Among the practical points noticed in the first section 

 of the work are the following : That the red or black mul- 

 berry produces more vigorous worms than the white ; that 

 the old notion of selecting bright-coloured cocoons for 

 breeding has given place to the belief that dull yellow are 

 the best ; that the practice of limiting the time of copula- 

 tion of moths is injurious ; that while the worms are making 

 their cocoons, the ventilation of the buildings, too often 

 neglected, is even more important than warmth. The 

 symptoms of the disease known as Pebrine are detailed, 

 but its cause seems to be not known. That its recurrence 

 coincides with unusually wet and cold seasons is esta- 

 bUshed, but whether it results from a parasitic vegetation 

 whose germs are carried in the air is slill a subject for 

 experiment. When the external indications are well 

 marked, the silk reservoir is found much diminished in 

 volume. The spots which appear on the skin continue 



