NATURAL PHILOSOPHY. 155 



in October last made a series of observations on the Lake of Ge- 

 neva to ascertain whether the effects of nocturnal radiation, tend- 

 ing to produce a gradual increase of temperature on ascending above 

 the earth's surface, are entirely dependent on the radiation of the 

 ground, properly so called, or whether they are equally perceptible 

 above a large sheet of water. 



With mercurial thermometers capable of showing a tenth part of 

 a degree (Centigrade), the temperature of the air at three inches, 

 six feet, and fifteen feet above the surface of the lake was examined, 

 the observations being made at the distance of about six hundred 

 yards from the land^ during exceptionally fine weather. Compara- 

 tive observations were made at the same moment on the borders of 

 the lake within a few feet of the water, and in the centre of a large 

 field about seven hundred yards from the lake. The average results 

 of these observations are given in the following table, the tempera- 

 ture being expressed in Centigrade degrees : 



Lake. Shore. Field. 



Surface 12. 9.90 6.98 



Three inches 11.65 10.40 8. 



Six feet 11.62 10.55 9.10 



Fifteen feet 11.80 10.62 9.65 



From these observations Marcet draws the following conclusions : 

 1. The gradual increase of temperature occurring on ascending 

 through the lower strata of the atmosphere, which appears con- 

 stantly to prevail on land about and after sunset, is not apparent 

 above a large surface of water. 2. The immediate vicinity of a 

 large sheet of water is sufficient to modify to a considerable ex- 

 tent the effects of the nocturnal radiation of the earth, and there- 

 by materially diminish the increase of temperature observed under 

 ordinary circumstances on ascending above the surface of the ground. 

 3. A striking difference (amounting to between two and three Centi- 

 grade degrees) is constantly observed between the temperature of the 

 atmosphere a few feet above the ground, and that of the air at the 

 same height above a large sheet of water. 



SPECIFIC HEAT AND CHEMICAL COMBINATION. 



At a late meeting of the London Chemical Society, a paper was 

 communicated by Mr. J. Croll, on the above subject, of which the 

 following is the substance : 



After alluding to the opinion generally held with reference to the 

 specific heat of compounds, compared with that of their component 

 elements, namely, that a diminution took place during combination 

 unless the resulting compound was a fluid, in which case the spe- 

 cific heat was increased, he stated that he had found this was not 

 correct ; for that the specific heat of compound gases and liquids was 

 generally less, and that of solids more, than that of their component 

 elements. A table of the specific heat of different bodies had been 

 drawn up, from which it appeared that out of ninety-four solid com- 

 pounds, the specific heat of sixty-six had been increased, and of 

 twenty-eight diminished, by combination ; out of twenty-eight gases 

 there was an increase with six, and a decrease with twenty-two ; 



