1896.] MICROSCOPICAL JOURNAL. 347 



at the central rays of light on the Podura scale to bring 

 them out. And microscope makers, or rather the makers 

 of objectives, Charles Spencer, Robert B. Tolles and Will- 

 iam Wales in this country; Powell, Lealand, Smith and 

 Beck in Europe, were then prominent. Charles Spencer 

 was the prince and was followed close after by Robert 

 B. Tolle's. 



We had diatoms on the slides, as Pleurosigma angula- 

 tum, and we had them living, but how to study theuj and 

 keep them living was a problem. Prof. Smith made an 

 ingenious contrivance for keeping them alive and study- 

 ing them whilst so alive and it was known as a growing 

 cell. Grrowing cells had been made in England, but none 

 of them were trustworthy. Smith's answered the jjur- 

 pose admirably, only there was one defect. It had to be 

 made with too many joints, which soldered with a cement 

 would leak and let tlie water out just at the time when 

 it was wanted. So I propounded to George Wales what I 

 wanted and this was the result. 



A piece of plate glass about a quarter of an inch thick 

 was taken. It was three inches square. In the centre by 

 means of a lathe set with a brass cylinder and fed with 

 water and emery, a hole was cut about two inches in 

 diameter. The mode by which it is cut is known to those 

 who use a lathe and is by soldering the plate glass on 

 another plate of glass and holding it against the revolv- 

 ing cylinders. In this manner the glass plate is bored 

 with a hole through it. It is then taken ofl" the plate it 

 was fastened on and cleaned. This forms the box of the 

 growing cell. A bottom is formed of plate glass, three 

 inches square but only ordinary plate glass. It may be 

 about one sixteenth of an inch thick. It is soldered to 

 the bottom of the cell ordinarily. But sometimes I find 

 it is not necessary to solder it. It keeps in place without 

 so doiuo;. The solder or cement is rubber cement or 



