192 
used ; and to correct residuary aberrations of the objective, 
and at the same time amplify, Dr. Pigott has introduced an 
important adjustable combination between the eye-piece and 
the object-glass. There seems to be considerable reason for 
the step proposed by Dr. Royston Pigott. Just as great 
results were obtained in passing from the single lens or com- 
bination to the compound microscope of eye-piece and objec- 
tive, so by adding distinct integral factors to these two, such 
as Dr. Pigott’s “aplanatic searcher,’ we may obtain excel- 
lences quite impossible by any amount of attention bestowed 
on the objective alone, or only with difficulty reached by long 
labour, leading to very high price for high powers. 
Dr. Pigott has, during the past year, published some 
account of his researches in the ‘ Quarterly Journal of 
Microscopical Science,’ and has communicated papers to the 
Royal Society, one of which is about to appear in the 
‘ Philosophical Transactions.’! 
Naturally at first the makers in London and the Micro- 
scopical Society were sorely tried by Dr. Pigott’s exposure of 
the Podura-scale, but we hear, as one good result already 
obtained, that Messrs. Powell and Lealand have constructed 
a new 1-8th, both dry and immersion, with great care, which 
is declared to be the best glass yet made. It has been pro- 
posed to form a committee for the purpose of examining 
carefully as to penetration, definition, and angular aperture, 
the best glasses of our English makers, the best American 
glasses, and the best of Hartnack’s, Gundlach’s, and others, 
the glasses being mounted similarly, with private marks only 
for recognition, so as to prevent all possibility of prejudice 
on the part of the committee. Were this done, the result, 
whichever way it tended, would be eminently satisfactory. 
Of this the writer is sure, that many persons—even eminent 
microscopists—have made up their minds about the qualities 
of foreign objectives, without having seen any, or only very 
poor examples, and then when a really fair specimen of such 
a glass is placed before them, they exclaim with astonishment, 
“ Why, this is the finest glass I have ever seen.” We shall 
be glad to receive suggestions or assistance in carrying out 
the proposed comparison of objectives. Dr. Royston Pigott 
has expressed his willingness to aid in such an undertaking. 
E.R. L. [Nature.] 
The Microscope in the Study of Rocks.— Professor Archi- 
bald Geikie contributes to ‘ Nature’ (February 9th and 
16th) two elaborate reviews of ‘“ Recent Petrographical 
1 See p. 166 of the present number of this Journal. 
