96 CORKESPONDENCE. 



is sufficiently fluid to drop nicely from the neck of an ounce vial. He 

 prepares the objects in tlie usual way, soaks tbem in turpentine from 

 a few minutes to several weeks, according to tlie nature of the object, 

 then places them on the slide, drops the balsam on, covers with small 

 round glass, and sets aside for some days ; by the end of this time, 

 which varies according to the nature of the object, all the air-bubbles 

 will bave made their way from under the glass, unless actually en- 

 closed in the substance of the object, which indicates either too short 

 time in the turpentine, or, in some cases, the absolute need for the use 

 of an air-pnmp. The slides can be left in this state until these are 

 sufficient to bake, which he manages in the following way : — He has a 

 tin or copper box 12 inches square by 2V inches deep, flat on the top : 

 this holds three dozen slides. He fills the box with water, places the 

 slides on the top, and on each a flat bullet or large shot. He then 

 puts a gaslight under the box, and keeps the water nearly boiling for 

 about forty-eight hours : the slides will then be sufficiently baked, 

 and may be cleaned and finished ofi" by putting a ring of black or 

 other varnish round the edge of the glass circle. He found the use 

 of the spring clips very objectionable, as he was always getting too 

 much or too little pressure on his slides ; but by having various sizes 

 of bullets and shot, he can put just the weight he requires on each 

 slide. The bullets are flattened by striking them with a hammer. 

 This process prevents all possibility of getting the balsam to the 

 boiling point, and at the same time gives as much heat as is required. 

 He has exchanged many slides with correspondents, who have, with- 

 out exception, expressed a very favom-able opinion of them. He 

 should say that, if the object is very thick, and consequently the 

 balsam thick round it, it should bake rather longer. The two funnels 

 are merely to allow of the expansion and contraction of the water as 

 the heat varies. His objections to Mr. Kitten's plan (though in his 

 hands, no doubt, through practice it is successful) are that air, if it 

 gets in, will be difficult to get out, instead of going out itself, as in his 

 plan ; that it affords no opportunity of carefully examining the object 

 when on the glass to remove any dust or hairs ; that the wire clip 

 will often crush a valuable object, or not subject a strong object to 

 sufficient j)ressure, and that the slide will sometimes get too hot over 

 the lamp and s^joil all the work. 



COEKESPONDENCE. 



Erratum in Mr. Tolles' Article in May Number. 



To the Editvr of the ^Monthly Microscopical Joarnal^ 

 Sir, — In your Journal for May last, p. 213, there is an error. 

 Fourth line from the top, for " closest " read " At closed, to the extent 

 of one-half of its whole adjustment." 



Respectfully yours, 



ROBT. B, TOLLES. 



