the Air 'Thermometer. 341 



1, 2, 3, 4s 5, 6, &c. 



2, 4, 8, 16, 32, 64, &c. 



the upper being the additional heat, and the lower the ratio in 

 which the force is augmented. But all this is on the supposi- 

 tion that the density does not increase with the temperature ; 

 whereas the density of steam in a state of saturation, augments 

 in a ratio almost as much above the second of these series, as 

 that exceeds the first. Now the temperature of all elastic fluids 

 is increased by condensation ; that is, the same weight of steam, 

 at a given temperature, contains less heat as its density is greater. 

 These arguments, I presume, would more than account for the 

 saving of heat which experiment indicates ; and, for this rea- 

 son, they are the more satisfactory, because high pressure en- 

 gines work under many disadvantages, the greater excess of 

 their temperature above that of the ambient air subjects them 

 the more to its cooling influence. 



From what we have seen above, it is extremely probable that 

 the absolute quantity of heat in bodies is very great. This con- 

 sideration may assist in accounting for the heat which becomes 

 sensible in the case of friction, of chemical combinations, elec- 

 trical phenomena, combustion, respiration, and in many of the 

 other operations which take place in the economy of nature. 



The chief points discussed in this brief essay are highly im- 

 portant in the doctrine of heat; and when once it is known that 

 they admit of such proof, I expect to see them investigated dif- 

 ferently, and no doubt with improvements. 



Observations on the Structure of some Silicious Sponges. By 

 R.E. Grant, M.D., F.R.S.E., F.L.S.,M. W.S., Honoraiy 

 Member of the Northern Institution, &c. Communicated by 

 the Author. 



JL HE existence of silicious spicula in sponges, and in other 

 genera of zoophytes, has been long known. Pallas sixty years 

 ago described the Alcyonium au7'antium, Alcyonium cotoneum, 

 and Alcyonium ashestinum, as composed of minute asbestine 

 needles, which he compares in hardness to pumice (El. Zooph. 

 p. 344, 357, 360.) Ellis seventy years ago, Gmelin, Lamou- 



