The National Microscopical Congress. 63 



tions, is not far from one-5o,oooth of an inch for eleven intervals. For 

 a large number of intervals the deviation will be somewhat larger, but 

 it will not be proportional to the number of intervals. 



3. A single observer can obtain an agreement with a normal equation 

 representing all the observed values, as far as a solution by least squares 

 can represent them, within somewhat smaller limits than those ob- 

 tained by comparing the results obtained by two different observers. 



A paper was then read from Mr. C. C. Merriman, of Roches- 

 ter, entitled 



"some new forms of mounting." 

 Shellac cement is the favorite with the author for making 

 cells, either for dry objects or for such as are to be mounted 

 in balsam in a cell. Anilin colors are used for ornamenting in 

 preference to all others. One method of mounting, which 

 gives fine results with certain objects, deserves notice, and we 

 give it in the author's words. 



" If the objects to be mounted will bear immersion in balsam, as 

 shells, plant seeds, minerals, etc., I pursue the following plan : The 

 thin glass covers are cemented to some old slips, which are kept for the 

 purpose, by two or three touches of balsam applied at the edge of the 

 cover. Care is taken in this, and in all cases, to accurately center all 

 work on the slides by means of the self-centering turn-table. Then, on 

 a light coating of balsam in the center of the cover, the objects, what- 

 ever they may be, are placed and arranged. When quite dry, and the 

 objects are thus securely fastened, they may be completely covered by 

 balsam and put into the dry-oven until thoroughly hardened. Then 

 over the balsam Brunswick black, if the objects are white, or white 

 zinc cement, if they are dark or high-colored, may be spread by thin 

 layers at first, each being dried in the open air for a day before the next 

 is applied, until there is no opaque covering to the objects. The thin 

 glass cover is now thoroughly cleaned around the objects and then re- 

 moved from the slips by a slight heating just sufficient to loosen it. It 

 can then be turned over and mounted on the cell designed for it. The 

 best preparation for fastening the cover to the cell is gelatine dissolved 

 in water, with enough alcohol added to liquefy it from the jelly state. 

 Just enough of the water cement seems to run in under the glass, and 

 to dry just where it is placed. Afterward the cell maybe finished with 

 liquid balsam, carefully avoiding the little aperture, and the outer edge 

 gathered up into a neat, trim little circle with the point of a knife on 

 the turn-table." 



This method of mounting in balsam on the cover, and 

 backing up with black varnish, deserves to be better known. 

 We have seen some of Mr. Merriman's slides made in this way, 



