1098 SUMMARY OP CURRENT RESEARCHES RELATING TO 



shrinkage. If care, however, is exorcised, satisfactory results can bo 

 obtained with glycerin-jelly. The object should bo first soaked in 

 diluted glycerin, and properly deposited in its cell. After the cover 

 is put on, a ring of balsam aud benzole should bo applied and allowed 

 to harden ; the slide is then to bo well washed under the tap, and a 

 ring of shellac varnish added. Another washing and another coating 

 of shellac follows, and then the object is to be more permanently 

 varnished with successive coats of gold size laid on as thinly as 

 possible. Slides so prepared will last upwards of 25 years. 



Needle for manipulating objects immersed in Canada Balsam. 

 — Mr. J. Joly (B.E. Trinity College, Dublin) writes : — The accom- 

 panying sketch (fig. 247) depicts an easily made contrivance, which 

 has been of much service to me in arranging minute crystals in 

 Canada balsam. A warm needle is essential for this kind of work 



Fig. 247. 



unless the balsam be rendered very thin with a solvent, but the latter 

 plan is inconvenient with lunipy objects, which will soon be left pro- 

 truding by the very thin balsam, and the addition of more balsam 

 subsequently is very likely to disturb the arranged objects. I found 

 it necessary to work in thick balsam, keeping the needle hot by 

 inserting it frequently in a spirit flame, taking care to withdraw it 

 from the balsam before it had fallen to the solidifying or thickening 

 point of the balsam. This was an arduous way of proceeding, and 

 led me to devise a needle which would stay hot without any attention 

 from the manipulator, and the temperature of which would be 

 adjustable. 



To this end the needle is so mounted that the current from a 

 small bichromate cell may be passed through a portion of its length, 

 the point becoming warm by conducting heat from the portion 

 traversed by the current. The arrangement will, I hope, be under- 

 stood from the figure. A wooden or ivory pen-handle is drilled 

 axially to receive a brass wire, one end of which is connected with 

 one of the binding screws affixed at the end of the handle, the other 

 end is split to receive the head of the needle at d in the figure. A 

 barrel, with a spring forceps, clips the needle at c ; this barrel is 

 electrically connected with the second binding screw on the handle 

 by a fine copper wire a b let into the handle along its whole length. 

 A current entering at one binding screw traverses the length c d of 

 the needle and leaves by the second binding screw. 



I find that with this arrangement a needle one-half larger than that 

 figured may be kept sufficiently hot when the plates of a one pint 

 bichromate cell are about one-half immersed ; the temperature is 

 adjustable to a nicety by letting down the plates more or less. Very 

 fine spirally coiled wires do for connections and do not interfere with 



