88 
Farrants^ on a Micrometer Object-finder. 
vicula Smithii (olim elliptica, Sm.)^ very fine. Himantidium 
majus, large. All these occur^ with some commoner forms, in 
the coarser densities, along with the larger of the new forms. 
I shall be glad to supply observers with the Glenshira 
Sand in its natural state ; and would recommend them, after 
it has been boiled in acid, to separate it into densities in the way 
described by Mr. Okeden. The coarsest portions in which any 
forms occur, contain so few as to be worthless. The next 
densities contain the forms above enumerated, as well as the 
larger among the new forms, with others; and the finer densities 
contain all the middle-sized and small forms. When well 
prepared, the entire Amphora Grevilliana, for example, is by 
no means rare in the coarser density, where it is accompanied 
by A. Arcus, Campylodiscus simulans, Navicula maxima, N. 
formosa, N. latissima, Eupodiscus sparsus, E. Ralfsii, ^c, ^c. 
P.S. — I find I have omitted to mention two species, which 
are admitted in vol. ii of the ^ Synopsis,' as British forms, 
and which occur in this deposit. These are Navicula Lyra, 
Ehr., and N. retusa, Breb., both marine forms. 
I must take this opportunity of expressing my obligations 
to Mr. West for the great pains he has bestowed on the 
engraving of the numerous figures above described. 
A Micrometer Object-finder. By R. J. Farrants, Esq. 
(Read April 30th, 1856.) 
A sure and ready method of determining the position of a 
microscopic object on the glass slide which contains it, so 
that it may be registered, and the object be brought into the 
field of view of the microscope, at any time and with any in- 
strument, is still a desideratum with microscopic observers. 
Ingenious suggestions have indeed been off'ered, from time to 
time, with a view to supply this want ; but that none of them 
have fulfilled the requirements may be inferred from the fact 
that no one of them has obtained general acceptance. I do 
not doubt that an object may be found, if its place on the 
glass slide has been accurately registered, with any of the 
"Finders" at present before the public; still, though the 
result may be sure, with none of them is the method of de- 
termining the position of the object, in the first instance, of 
ready application. 
The plan of Mr. E. G. Wright, of Hereford, published in 
the ' Quart. Journ. of Micr. Science,' vol. i, p. 301, consists in 
fixing to or engraving upon the stage of the microscope two 
scales at right angles to each other, and reading ofi* from 
