126 M. Lewy on the Constitution of the Atmosphere. 



at the end of which the new and full moons happen on the 

 same days of the year as they did at the beginning, is very 

 remarkable, for by it Christians have always ascertained the 

 days of their movable festivals, and the Greeks adopted it 

 for the like purpose in 433 B.C., Meton having obtained the 

 first prize at the Olympic games for its discovery. Now 

 Meton may have derived it through Hecatceus from Britain, 

 as above-mentioned, and the British Druids may have had it 

 from the Jews, whose year in the time of Moses consisted, 

 like our own, of 365 days, and whose great festival of the 

 Passover was (like ours of Easter) regulated by the moon. 

 It is, I imagine, to this cycle of nineteen years that the num- 

 ber 19, so prominent in our Druidical temples, refers. 



On the Constitution of the Atmosphere. By M. Lewy. 

 Read to the French Academy of Sciences. 



The memoir which I have the honour to submit to the 

 Academy contains the results of a series of researches on 

 the constitution of the atmosphere, executed between France 

 and New Granada, and from the coast up to 3193 metres 

 above the level of the sea. 



The analyses were performed by the new process of M. M. 

 Regnault and Reiset, which consists, as is well known, in 

 analysing the air by volumes. To measure the elastic forces 

 of the gas I employed an excellent cathetometer, constructed 

 by M. Perraux. The process thus combined enables us to 

 obtain much greater precision than has hitherto been reached 

 in this class of experiments. To judge of the degree of ac- 

 curacy attainable, it suffices to examine the numerical details 

 of two analyses ; and it will be seen that the greatest differ- 

 ence between two analyses made with the same specimen of 

 air never exceeded To,otroth, and most frequently was not 

 more than Tffir,V?r^th. 



The various specimens of air which I analysed were col- 

 lected in bulb tubes with the two ends drawn out and open ; 

 the capacity of these tubes was about 100 cub. centims. The 

 air was collected in the following manner : one of the extre- 

 mities of the tube was connected by means of caoutchouc 



