2P>6 On a Method of ascertaining Magnifying Power 
through those published articles of his which I have seen. He 
teaches much, and suggests more. 
The use of this eye-piece is not confined to the microscope. It 
will measure the size of the image in the focus of the objective of 
the telescope ; also the breadth of the pencil emergent through any 
telescopic eye-piece ; and so lead to the magnifying power of the 
telescope. 
It also measures the distance apart of the Fraunhofer lines in 
the spectroscope ; and, of course, would show the relative dispersive 
power of any prism or combination of prisms. 
VII. —On a Method of ascertaining Magnifying Power and 
Minute Magnitudes by Miniatures. By Dr. Boyston-Pigott, 
M.A., M.D. Cantab., M.R.C.P., F.C.P.S., F.R.A.S., M.R.I., 
F.R.M.S., late Fellow of St. Peter’s College, Cambridge. 
That quaint old writer Dr. Kitchener says : — “ An easy way of 
judging of the relative magnifying powers of various eye-tubes and 
lenses is to hold them up about 12 or 18 inches from the eye, and 
three or four feet from a window — that in which the panes of glass 
appear least, magnifies most : or place two candles nearly together 
and hold the lenses about a foot from them, that in which the 
candles appear nearest together magnifies most.” 
Upon this principle I now propose the following simple method 
of ascertaining the magnifying power of an object-glass, which I 
call the miniature method. 
Place the object-glass in the position of a condenser. At exactly 
ten inches from the stage adjust a scale of inches and tenths. Bring 
the image of the scale upon a ground-glass slide, with its ground 
surface downwards. The ground glass now shows a miniature of 
the scale. Now replace it by a micrometer slide, and viewing it 
with a low power,* readjust the condensing object-glass so as to 
bring the image of the scale into a focus accurately coincident with 
the divisions of the stage micrometer. The actual size of the minia- 
ture scale can be read off upon the stage micrometer, which imme- 
diately gives the amount of diminution, and therefore of the 
enlargement. 
Ex. (1). A micrometer on stage showed a tenth on scale mi- 
niatured by an object-glass to be 19 thousandths. The magnifying 
power therefore 
- 1 19 
~ To ' iooo 
= 100 -i- 19 = 5-26. 
A power of 100 is convenient. 
