on ice-making and ice-machines. 



373 



analogy to the cosmical nebula? revealed by the 

 spectroscope. Further, we have to bear in miud 

 that all those original comites of the sun which, 

 forced into hyperbolic and parabolic tracks, have 

 quit the system, must likewise be added in order 

 to fill up the space circumscribed by Neptune's 

 orbit. In this way we arrive at a leastwise con- 

 ceivable degree of attenuation for the primordial 

 matter of the solar system. 



If we consider that the fixed stars, too, have 

 their attendant planets ; that in their systems 

 the same process of elimination takes place ; and 

 that our sun receives from the neighboring fixed 

 stars at least as many banished members of other 

 systems as have been eliminated out of its own, 

 it will be seen that we can only proximately and 

 indirectly determine the number of the planetary 

 bodies which have been dropped from our sys- 

 tem. 



Those comets and meteorites which travel in 

 a retrograde direction are to be regarded as in- 

 truders from other systems. Some of these, 

 under the action of planetary influences, have 

 acquired closed orbits, and have settled for good 

 within our system. As for the comets and me- 

 teorites with direct motion, though their elon- 

 gated orbits do not prevent us from recognizing 



them as fragments of planets that once belonged 

 to our system, we nevertheless have still to ac- 

 count for the fact that whereas the orbital planes 

 of the planets are nearly coincident with the 

 plane of the sun's equator, the orbits of many 

 comets and meteorites form considerable angles 

 with the plane of the earth's orbit. But this 

 difficulty vanishes also when we regard this in- 

 clination toward the orbit of the earth as pro- 

 duced by perturbations. Thus, for example, 

 Brorsen's cometof 1846, which, according to d'Ar- 

 rest, in 1842, the attraction of Jupiter brought 

 nearer to us, had to the earth's orbit an inclina- 

 tion of 41°, which was reduced to 31° by this 

 single perturbation. Under suitable conditions, 

 that angle might be increased to the same extent. 



It is plain, therefore, that we can reach a 

 monistic conception of the history of our solar 

 system only by assuming indirect selection of the 

 fittest and elimination of the unfit here as in 

 every other province of Nature. In this way not 

 only do we explain the teleological distribution 

 of mass through the planetary system, but also 

 obviate the necessity of having a separate theory 

 each for planets and comets. 



So must we supplement Kant and Laplace 

 with Darwin. — Kosmos. 



ON ICE-MAKING AND ICE-MACHINES. 



By W. N. HARTLEY, F. E. S. E. 



THE resolution of all forms of energy into 

 heat, the continual passage of heat through 

 solids, liquids, and gases, and its tendency to be- 

 come equally distributed through all matter, are 

 now recognized as facts; hence the inevitable 

 conclusion that finally all substances in the solar 

 system, if not in the universe, will ultimately ar- 

 rive at one common temperature. Mechanical 

 motion, electricity, chemical action, all other 

 forms of energy which at present are sources of 

 heat, will be completely exhausted. Man, by his 

 use of machines, is hastening this end of all 

 things, and this indeed by the production of low- 

 as well as of high temperatures. 



An economical means of freezing water is a 

 fruitful source of profit at the present time, for 

 the manufacture of ice serves not only the pur- 

 pose of enhancing our bodily comfort in summer, 

 but also for rapidly cooling large volumes of 

 liquid, as in the operation of brewing and other 

 industrial processes, and for the better preserva- 



tion of animal food in seasons and climates which 

 hasten putrefactive changes. 



The difficulty experienced in freezing water is 

 due to the very large amount of heat it must lose : 

 1. In being lowered to the temperature of 32° 

 Fahr. ; and, 2. In being changed from liquid water 

 at 32° Fahr. to solid ice at the same temperature. 

 The first quantity is called its specific heat, and 

 the second is its latent heat. These quantities 

 are greater for water than for any other sub- 

 stance ; hence the cooling power of ice is greater 

 for any given temperature than that of any other 

 body, and the cooling power of water is greater 

 than that of any gas or liquid. Faraday calcu- 

 lated that the heat absorbed during the conver- 

 sion of a cube of solid ice measuring three feet 

 in the length of one side, into liquid water with- 

 out undergoing any rise of temperature, would 

 require the combustion of a bushel of coals for 

 its artificial production. 



It is evident from these statements that, in 



