TOTAL SOLAE ECLIPSE OF JULY 18, 1860. 
351 
verbally, at one of the meetings of the Astronomical Society, and which was in con- 
sequence adopted by Mr. Peitchaed. No account having been published of this 
appendage, and experience having proved its value in eclipse observations, I think it 
desirable to describe it here. It vdll be remembered that Mr. Hodgson some time ago 
proposed that a piece of polished glass should be used as a diagonal reflector in observ- 
ing the sun ; and “ Hodgson’s solar eyepiece ” has been generally adopted, and is a 
most convenient and efiicient instrument. It occurred to me, that if the glass reflector 
were made in the form of a parallelogram, of such dimensions that a moiety of its sur- 
face would sufllce for the field of the telescope, one-half of the upper reflecting surface 
might be silvered and the other left plain, and that the addition of a suitable con- 
trivance would enable the observer to draw into position the unsilvered or the silvered 
surface, according as either partial or total reflexion might be required. The silver 
film is so extremely thin that it in no way affects the focus, yet it is susceptible of the 
highest possible polish. It was not a convenient plan to silver only half the mirror ; so, 
when the whole had been silvered *, one-half of the silver was neatly removed by means 
of a cloth, wetted with cyanide of potassium, strained over the forefinger. The rough- 
ened back of the reflector was freed from silver, and the plate then washed thoroughly 
with distilled water and allowed to dry. A little pad of wash-leather, well charged 
with dry rouge by rubbing it on a second piece of leather on which some rouge-powder 
had been placed, very soon removed the peach-like bloom from the silver surface, and 
produced a perfect polish. 
The construction of the eyepiece will be readily understood by reference to the 
accompanying wood-engravings, wherein the same letter refers always to the same part. 
Fig. 1 is a front view, the plain glass reflector being in operation. Fig. 2 is a view of 
the under side, the plain glass being still in position for use. Fig. 3 shows the glass 
* A method for silvering glass has been described by myself and Dr. Mullee in the 
of the Astronomical Society,’ vol. xix. p. 171. 
3 B 2 
Monthly JNotices 
