460 NaturaUPhilosophical Collections. 



temperature at the moment on the earth's surface ; the other, npmely the tempe- 

 rature of the planetary space, is constant, even in regard to the time. 



" The numerical solution pre-supposes accurate observation^ of temperature at 

 isolated points to a considerable height above the earth's surface, which, however, 

 are unfortunately so extremely few, that we can have recourse among newer ob- 

 ■ervationsbut to a single one, that of Gay-Lussac, in his aeronautic expedition. It 

 were to be wished that the same experiments were repeated particularly in the 

 neighbourhood of the equator, where the oscillations around the mean state of the 

 atmosphere, and consequently the prejudicial influence of accidental circumstances, 

 are less to be dreaded. In the meantime, availing myself of this observation, I 

 have obtained for the planetary space a temperature of — 49.85 Cent, which dif- 

 fers only by l-7th of a degree from the result of Fourier, deduced from the laws of 

 heat radiated from the mass of the earth, the temperature of which he supposed 

 to have reached its asymptotic state of absolute unchangeableness on the whole. 

 Without believing in the identity of light and heat, or in the certainty of our 

 photometric knowledge, I have thought it not entirely voi4 of interest to see what 

 result, in relation to this point, could be obtained from Lambert's statements, in 

 gard to the absorption which takes place in a ray of light passing from the zenith 

 through the whole atmosphere, calculated on the supposition that the differen- 

 tial of the increase of temperature is always proportional to that of the so absorb- 

 ed light. By this process I have obtained for the required temperature — 50°35. 

 I was most agreeably surprised by so remarkable an agreement between both of 

 these results and that which Fourier derived from principles so different ; and it 

 affords an additional reason why the function I have given for the temperature 

 should be taken into due consideration. The immediate results of the same are, 

 that the temperature diminishes with a constantly diminishing velocity, as we as- 

 cend in the atmosphere, and that even at a given height, this velocity is greater 

 the higher the temperature at the earth's surface. 



" Without having in view any examination of the formula for determining 

 heights by the barometer, I have, in the application of them to the observations of 

 Gay-Lussac, shown, that in the determination of heights so uncommon as that of 

 Gay-Lussac, causes of error may intervene, which, in the case of lower and more 

 common heights, it is not necessary to take into account. To me that function 

 is of importance, since irom it I have derived a function for the refracting powei 

 of the atmosphere at all points of the trajectory of light, and I have, by way of 

 preliminary, treated in considerable detail the formulae derived from it, for the de- 

 tinitive determination of the refraction itself, in which I have proceeded so far 

 that I have at last commenced the purely mathematical investigation of the re- 

 quired problem, such as it becomes after the strictest discussion of all the physical 

 points connected with \t,"— Johnston's Analysis of Berzeliiis' Arsber'dttelse. 

 Rrewster's Journ, No. V. N. S. 



On the Artificial Formation of Urea ; ly Wohler This is one of those 



rare results which approximate the productions of art to those of nature, and lay 

 open the possibility of imitating her in some of her elaborations, though they un- 

 fortunately afford little ground for the flights of those airy speculators who hold 

 up the probability of our being soon able to dispense altogether with the agency 

 of nature in the production of the animal and vegetable substances, upon which 

 we at present depend for our existence. 



If Cyanite* of silver be treated with a solution of sal-ammoniac, or cyanite of 

 lead with caustic ammonia, there is formed, instead of cyanite of ammonia, a 

 crystalline matter which has all the properties of pure urea, and which therefore 

 is Urea. 



• This is prepared with Wohler's acid, which we have shown must be called 

 the Cyanous, and its compounds, of course, Cyanites. 



