POUCHET, ON ATMOSPHERIC MICROGRAPHY. 189 



a glass, and within a space of two square millimetres, all the 

 particles disseminated in a cubic metre of the atmosphere, or 

 even more. 



By this new method we have proved once more a fact 

 which we had previously advanced. We have been enabled 

 to see that the spores of plants and the ova of Infusoria, as 

 has been equally recognised by MM. Joly and Ch. Musset, 

 were infinitely rare, even in situations where they might have 

 been expected to occur. Thus, in our laboratory, where 

 almost throughout the year microzoa and nmcedinous fungi 

 are continually pullulating, I have been unable, in 1000 cubic 

 decimetres of the air of which I have concentrated the invi- 

 sible corpuscles by the aid of my instrument, to find a single 

 infusorial ovum, nor a single spore. 



The volume of air, however, just stated is erroneous, when 

 compared with the small quantity necessary to produce an 

 abundance of proto-organisms. In fact, whenever a suitable 

 infusion is employed, and placed in contact with not more 

 than a cubic decimetre of air, that is to say, with the 

 thousandth part of the volume explored, millions of Infusoria 

 or of Cryptogamia are almost always sure to make their 

 appearance in it. 



The instrument which we employ to concentrate the 

 atmospheric corpuscles is constructed as follows. It is 

 formed of a glass tube, closed hermetically at each end by 

 copper stop-cocks. The upper stop- cock, which is fixed, 

 receives a copper tube, terminated exteriorly by a very small 

 funnel, whilst internally it is drawn out into a very fine point, 

 the opening of which does not exceed 050 mm. in diameter. 

 By the lower stop- cock a flat, circular disc of glass is intro- 

 duced into the apparatus, which is placed at the distance of 

 one millimetre from the elongated point of the tube. The 

 apparatus is then closed, and the interior is placed in com- 

 munication with an aspirator, by means of a tube which 

 traverses the lower stop- cock. 



When the aspirator is put into action, the surrounding air 

 being sucked in, passes through the tube, and issuing from 

 its pointed extremity, strikes upon the glass disc, and deposes 

 on its surface all the atmospheric corpuscles contained in it, 

 precisely in the same way that in Marsh's apparatus the 

 metallic particles, issuing from it, are deposited on the plate 

 of porcelain. The more bulky particles all collect into a 

 small, central heap, which, however, does not exceed a milli- 

 metre in diameter ; whilst the others only radiate at a little 

 greater distance around it. 



When the glass which has thus received the jet of air is 



VOL. VIII. Q 



