J. D. HARDY ON A NEW VIVARIUM. 



213 



is held together either with strong indiarubber rings or springs. To 

 use it, take off the upper glass, and having cleaned both glasses, 

 place the object on the lower glass, manipulate it to the best advan- 

 tage, replace the upper glass, and then fill up with water through 

 the hole at the top. It will be found that the cell is reversible and 

 that it can be plunged into a beaker full of water in any position 

 without any fear of losing the object. 



"Receipts for Microscopists." — Correction. 



The Interpolation formuUe for Spectroscopic bands will be found 

 in " Watts' Index of Spectra," and not in Suffolk's work as stated. 

 They also appear in *' Silliman's Journal " for July, 1870, in which 

 W. Gibbs first jjublished them. 



In Number IV. of the " Receipts " it is stated that the mono- 

 chromatic bull's-eye condenser is of '' unusual " form. It should be 

 " of the ' usual' external shape," and differs from ordinary ones only 

 in being hollow, so as to receive coloured liquids between the plane 

 and convex surfaces. 



