I02 



A CONTINUOUS RECORD OF ATMOSPHERIC NUCLEATION. 



I therefore endeavored to ascertain whether the particles might not be 

 made visible directly. The chances of success seemed small indeed, particularly 

 as Assmann had failed to see the particles with magnifications of even 400 

 diameters. But after long trial, the resvilt was eventually accomplished in a 

 way that now seems surprisingly simple. 



The compound microscope, M, magnifying about 100 diameters, is pro- 

 vided with a filar ocular micrometer, n. The objective and the whole lower part 

 of the microscope is submerged in the condensation chamber, being stispended 

 for this purpose from the wide rubber cork, C. All lenses below C are her- 

 metically sealed with wax. The microscope originally carried a rigid stem, r, 

 to which were attached the plate, s, to be examined, the mirror, in, and the 

 metallic disc or shield, p. Afterwards the more flexible adjustnient shown in 

 the figm-e and described below was adopted. The low^er side of p, which is flush 

 with the objective, and the upper side of 5 are covered with wet blotting-paper, 

 the latter being perforated to admit light into the microscope through the thin 

 cover-glass placed at 5 and held sharply in focus by a suitable clip. The field 

 within which drops are to be counted is bounded at pleasure by the wires of the 

 micrometer. 



Figure i. — -Micrometric Apparatus. 



This apparatus was totally unsuccessful. Drops were but rarely seen to 

 fall on exhaustion, while the dew soon gathered on the plate, s, in such a way 

 as to be easily mistaken for droplets; for the dew evaporates like the latter 

 when the microscope is removed, and the regularity of the pattern on the plate 

 is the only distinguishing feature. 



