SCIENCE. 



33 



It was found that the second form of experiment gave 

 the most uniform results ; the method by cooling being 

 less accurate, owing to currents of air in the room, etc. 



The results are embodied in the following Table :— 



(Rate of Heating from 25 to 50 .) 



Table I. 



Seconds occu- Total number 

 Pressure. Temperature. pied in rising of seconds 



each 5 . occupied. 



760 miliims. 25 o o 



25 to 30 15 15 



30 to 35 18 33 



35 to 40 22 55 



40 to 45 27 82 



45 to 50 39 121 



1 millim. 25 o o 



25 lo 30 20 20 



30 to 35 23 43 



35 to 40 25 68 



40 to 45 34 102 



45 to 50 48 150 



620 M.* 25 o o 



25 to 30 20 20 



30 to 35 23 43 



35 to 40 29 72 



40 to 45 37 109 



45 to 50 53 162 



117 M. 25 o o 



25 to 30 23 23 



30 to 35 23 46 



35 to 40 32 78 



40 to 45 44 122 



45 to 50 61 183 



59 M. 25 o o 



25 to 30 25 25 



30 to 35 30 55 



35 to 40 36 91 



40 to 45 45 136 



45 to 50 67 203 



23 M. 25 o o 



25 to 30 28 28 



30 to 35 33 61 



35 to 40 41 102 



40 to 45 55 157 



45 to 50 70 227 



12 M. 25° ■ o o 



25 to 3° 3° 3o 



30 to 35 37 67 



35 to 40 41 108 



40 to 45 58 166 



45 to 50 86 252 



5 M. 25° o o 



25 to 30 38 38 



30 to 35 43 81 



35 to 40 54 135 



40 to 45 71 206 



45 to 50 1 j 6 322 



2 M 25 o o 



25 to 30 41 41 



30 to 35 51 92 



35 to 40 65 157 



40 to 45 90 247 



45 to 50 165 412 



There are two ways in which heat can get from the 

 glass globe to the thermometer — (1) By radiation across 

 the intervening space; (2) by communicating an increase 

 of motion to the molecules of the gas, which carry it to 

 the thermometer. It is quite conceivable that a consider- 

 able part, especially in the case of heat of low refrangi- 



*M=millionth of an atmosphere. 



bility, may be transferred by "carriage," as I will call it 

 to distinguish it from convection, which is different, and 

 yet that we should not perceive much diminution of 

 transference, and consequently much diminution of rate 

 of rise with increased exhaustion, so long as we work 

 with ordinary exhaustions up to 1 millim. or so. For if, 

 on the one hand, there are fewer molecules impinging on 

 the warm body (which is adverse to the carriage of heat), 

 yet on the other the mean length of path between colli- 

 sions is increased, so that the augmented motion is car- 

 ried further. The number of steps by which the tempe- 

 rature passes from the warmer to the cooler body is di- 

 minished, and accordingly the value of each step is in- 

 creased. Hence the increase in the difference of velocity 

 before and after impact may make up for the diminution 

 in the number of molecules impinging. It is therefore 

 conceivable that it may not be till such high exhaustions 

 are reached that the mean length of path between colli- 

 sions becomes comparable with the diameter of the case, 

 that further exhaustion produces a notable fall in the 

 rate at which heat is conveyed from the case to the ther- 

 mometer. 



The above experiments show that there is a notable 

 fall, a reduction of pressure from 5 M. to 2 M. producing 

 twice as much fall in the rate as is obtained by the 

 whole exhaustion from 760 miliims. to 1 millim. We may 

 legitimately infer that each additional diminution of a 

 millionth would produce a still greater retardation of 

 cooling, so that in such vacua as exist in planetary space 

 the loss of heat — which in that case would only take 

 place by radiation — would be exceedingly slow. 



PROFESSOR HUXLEY ON EVOLUTION. 



At a recent meeting of the Zoological Society, among 

 the papers read was one by Professor Huxley on 

 the application of the laws of evolution to the arrange- 

 ment of the vertebrata, and more particularly mammalia. 

 The illustrations adduced were those of the history of the 

 horse, principally, so far as is known, from the work of 

 Professor Marsh on the Eocenes of North America. The 

 announcement of the paper had drawn together an un- 

 usually large attendance, as it was expected that the mar- 

 shalling of the facts in Professor Huxley's hands would 

 have great interest in practically substantiating the the- 

 ory of evolution, which, though foreshadowed by others, 

 took practical shape in the work of Darwin twenty-one 

 years ago. 



Professor Huxley began by saying: — There is evidence, 

 the value of which has not been disputed, and which, in 

 my judgment, amounts to proof, that between the com- 

 mencement of the tertiary epoch and the present time the 

 group ol the equidae has been represented by a series of 

 forms, of which the oldest is that which departs least 

 from the general type of structure of the higher mam- 

 malia, while the latest is that which most widely differs 

 from that type. In fact, the earliest known equine ani- 

 mal possesses four complete sub-equal digits on the fore 

 foot, three on the hind foot ; the ulna is complete and dis- 

 tinct from the radius ; the fibula is complete and dis- 

 tinct from the tibia ; there are 44 teeth, the full number 

 of canines being present, and the cheek-teeth having 

 short crowns with simple patterns and early-formed roots. 

 The latest, on the other hand, has only one complete 

 digit on each foot, the rest being represented by rudi- 

 ments ; the ulna is reduced and partially anchylosed with 

 the radius ; the fibula is still more reduced and partially 

 anchylosed with the tibia ; the canine teeth are partially 

 or completely suppressed in the females ; the first 

 cheek-teeth usually remain undeveloped, and when 

 they appear are very small ; the 01 her cheek-teeth 

 have long crowns, with highly complicated patterns 

 and late-formed roots. The equidae of the interme- 

 diate ages exhibit intermediate characters. With re- 

 spect to the interpretation of these facts two hypotheses 



