J. M. Blake — Picking Out and Mounting Diatoms. 535 



Art. XLIV. — Picking Out and Mounting Diatoms; by 

 John M. Blake. 



The art of selecting and picking out any considerable 

 number of diatoms from a spread which contains a variety of 

 species, and of arranging the selected diatoms successfully 

 for mounting, appears to be attained by comparatively few 

 persons. The methods by which successful results are secured 

 are not generally known. Many workers are able to select a 

 limited number of forms by the hand method of picking, but 

 this method requires great concentration and nerve control. 



Among the difficulties to be surmounted, or at least allowed 

 for, are the pulse beats that affect the hand, the high magnifi- 

 cation making the pulsations quite apparent. 



In 1895 the writer devised an apparatus which overcomes 

 many of the difficulties. This apparatus is a small pantograph 

 made of light wire. It reduces the motion of the hand 

 twenty-six times. It consists of a jointed parallelogram (P) 

 made of number 20 iron wire. This wire is flattened at the 

 points where the rivets are placed. This parallelogram 

 measures five inches on each side. Within this area, in one 

 of its angles, is built a minute parallelogram twenty-six times 

 smaller (s). This tiny parallelogram measures three-sixteenths 

 of an inch on each side. The apex of the larger outer form 

 (P) is coincident with that of the small inner member (s) and 

 rotates on the same rivet. This rivet also passes through a 

 short bit of wire and on this wire (P) can be rotated in its own 

 plane. This rotation gives (P) a horizontal motion ; while the 

 short bit of wire itself rotates in bearings which give an up 

 and down motion at right angles to the plane of (P), (P) 

 itself slips over and around the body of the microscope. 



The short bit of wire referred to has its bearings held 

 about one quarter of an inch above the stage of the microscope. 

 This leaves room for a glass slip one and one-half inches wide 

 and six inches long to move underneath. A piece of sheet tin 

 is bent so as to form a clip to spring over the farther edge of 

 the microscope stage, and to this piece of tin the bearings of 

 the short piece of wire are attached by supporting strips. 



In use, the diagonally opposite apex of (P) is to be held in 

 the hand and a short and finely pointed hair is attached by 

 wax to the corresponding apex of (s). This hair is the implement 

 for picking up the diatoms, and points in a downward direction. 

 The diatom -spread is made on a cover glass, and from this 

 spread the selections are to be made. 



This cover glass is attached by moisture to the first-mentioned 

 slip of glass. The cover glass to which the diatoms are to be 



Am. Jour. Sci.— Fourth Series, Vol. XXXVII, No. 222. -June, 1914. 

 37 



