50 CORRESPONDENCE. ete aoe 
while fully concurring with Dr. Higgins in his high estimation of 
Mr. Wales’ objectives, I am of the opinion that he (Dr. Higgins) has 
either made an error in his measurement of amplification (210 diame- 
ters with the No. 1 or A eye-piece), or that the ,4,th objective is very 
much underrated in magnifying power. All of Mr. Wales’ 54,th objec- 
tives which I have seen have been as near or nearer iths than ;,ths 
in magnifying power; and below I give a Table of amplification of 
such ,*;th objectives as are at hand; also two jths for comparison : 
acai Eye-pieces. 
Maker. aoe 1 2. 3 
— SS 
4-10 J. Zentmayer .. .. 75 130 210 400 
» Smithand Beck .. 60 135 220 415 
es VOUes Wes) Wes 135 125 205 390 
EN PV SIER cs! | Gs “n'a 110 175 300 535 
1-4 R.B.Tolles .. .. 120 200 325 615 
» Smith and Beck .. 75 210 340 650 
The measurements were made with a first-class stand and eye-pieces 
of Zentmayer, the image of a stage micrometer being thrown down by 
a Spencer’s camera lucida, and measured at just ten inches from the 
eye; cover adjustment for 125th cover glass. It seems to me that 
there should be some uniform standard adopted by the different makers 
of objectives, so that the 1th of one maker may not be as high as the 
4th of another maker; or a ;4,th of one be as high as a ith of another; 
or, still worse, a 3-inch objective of one maker of precisely the same 
power as a 2-inch of another maker, which was just the case with two 
objectives which I had about one year since. If the objectives did not 
differ any more than the first three in the above Table it would be 
an improvement. The amplification which Dr. Higgins gives to his 
yths is as high as the highest ith in the above Table—Epwin 
BickNeEtt, Salem. 
CORRESPONDENCE. 
Mr. StoppEr’s Letter. 
To the Editor of the ‘ Monthly Microscopical Journal. 
Dr. Henry Lawson, Boston, May 30, 1870. 
Dear Sir,—I have but just seen the Monthly Journal for May, 
my copies for April and May not having arrived yet. 
Please publish the following errata in my letter in the May num- 
ber :—Page 257, 13th line from bottom, 1868 instead of 1848 ; page 268, 
14th line from top, Bicknell for Micknell; page 259, 5th line from 
top, 19th band instead of 17th. 
- Yours most respectfully, 
CHARLES STODDER, 
