1880.] 



MICROSCOPICAL JOURNAL. 



20T 



(lenoniinatioii are given together. 

 The first two numbers designate 

 the focal lengths of the tield and 

 eye-lenses respectively, the last 

 number the equivalent focal length 

 of the eye-piece. 



" A - ' OR '' No. 1 " Eye-pieces. 



Beck, 



Crouch, 

 (irunow, 

 McAllister, 

 Merz, 



Powell & Lealand, 2^, i 

 Verick, xi 



Zentmayer, 

 French, 



2)4, 1^4 = 1.66. 

 2%, i}{ = x.6. 



2^, 1^ = 1.73. 

 2^, lys^i.gi. 



-1.79. 



'4, iX = i-46. 



2}^, ii4 = i.88. 



2rs, 1^=1.62. 



" B " <)u '' No. !> '' Eye-pieces. 



Beck, 1.75, .87 =1.16. 



Crunow 1-625, -^7 —^-^S- 



McAllister i^s, H = .89. 



Merz(N"i^.), 2, i. =1.33- 



Swift. 2, I =1.33- 



From the above figures it will 

 be observed that the equivalent 

 focal length of " A " eye-pieces 

 varies from 1.46 to 1.91, of " B " 

 eye-pieces from .89 to 1.38 and of 

 '' C '' eye-pieces from .47 to .92. 



It will readily be seen that the 

 present method of designating eye- 

 pieces, as " A, B, C," or as "No. 1, 

 No. 2," etc., conveys no definite in- 

 formation a.s to their magnifying 

 power. Mr. Bulloch does not claim 

 that the rule given above for calcu- 

 lating the focal lengths is accurate, 

 but the results are sufficiently exact 

 for practical purposes. 



A Series of Hints In regard to 

 Mounting. 



BY (!. M. VORCE. 



(Iarbolic Acid in Mounting. — 

 I find that an object which has 

 been macerated in potash can be 

 mounted in balsam without drying 

 by the following procedure. Take 

 the object from the potash solution 

 and arrange it on a glass slip, for 

 which pui*pose a piece of window- 

 glass two inches square is very con- 

 venient. If necessary wash it with 

 pure water, using a camel's hair 

 pencil if you wish, then drain away 

 the water and wipe around the 

 object, add strong potash solution 

 and after it has been in contact with 

 every part of the object for a few 

 minutes drain it away and again 

 wipe the glass as close around tlie 

 object as practicable. Add carbolic 

 acid (pure) in considerable excess, 

 and warm the slip gently ; this 

 causes the object to become opacjue 

 but do not be disconcerted by this. 

 After a time, say 15 minutes for a 

 small thin object, warm the slip and 

 pour of! the acid, and again wipe. 

 Add more clear acid and transfer 

 the object to a mounting slip, which 

 is easily done without injuring the 

 object as follows : Lay the slip on a 

 box or block of about its own widtli, 

 and half an inch or more in height, 

 pour the acid from the square slip 

 on to the middle of the mounting 

 slip and, reversing the square slij), 

 bring it down upon the drop of 

 acid, so that the object may fii-st 

 touch it when, with a little care, the 

 object will settle down into the acid 

 without being much, if at all, dis- 

 arranged. If necessary it is tlien 

 arranged under the dissecting mi- 

 croscope, and when brought into 

 the desired position, if it is clear 

 and quite transparent, the acid is 

 drained away, balsam added and 

 the mount completed. 



