George W. Holley

lens in then ground down and polished suffi-

ciently to test its homogeneity and purity of it

proves satisfactory in these particulars it is there

finished. The difficulty in the way of success

his in this if there is a line of striae a quarter of

an inch long or a speck the size of a small spot

so far beneath the outer surface of the disk that it

cannot be ground out, it isa failure. Nine

hundred and ninety nine thousandths of the glass

may be perfect, if the remaining one thousandth

is defective it spoils the whole. Mr. [Feil?] has

cast [pane?] glass enough, in the 19 experiments,

to have made a dozen perfect lenses if he could

have separated it from these -as to size-helping

is defects. In pouring the [motled?] glass into an

enclosed space, like a mould, there is no way

for the air to escape except though the orifice through which the glass is poured, and as the mould stands edge wise and is shaped like a spherical wedge it is hardy possible for the air to escape or for impurities, if there are lighter than the glass, to rise to the tops or, if they are heavier to settle to the bottom, as shown in this crude sketch. (Sketch is inserted here) Furthermore, the center of gravity of the mass does not coinicide with the centre of figure. This defect, however, is cursed by maninpulation of the surface. The reasonable certainity of securing success by the method of lens construction which I propose will be of once manifest on examination. The proposition is to cast the glass in rectangular molds from 12 to 15 inches long and 3 or 4

inches square, as shown in this rough drafr: In this form the centre of gravity The map will coincide with the of figure. All air bubles

5

that a strong force is required to separate them. This perfection of surface with the cement generally used to secure the adhesion of glass surfaces would insure the solidity of the mass. It is hardly possible that M. [Teil?] could have failed to secure perfect bars of glass, out of the large quantity made during his 19 unsuccessful experiments, to have made a dozen lenses of even larger size than he desired. It seems evident that much larger and more perfect lenses can be constructed by this new method than by any other. The misfortune is that those who have the time and inclination to investigate such subjects never have the pecuniary ability to practically demonstrate

the utility of their theories. If from the vast sums that are lying idle in our country we could procure the comparatively trifling sum of five score thousands of dollars we could extend our knowledge of celestial geography almost ad libitum and gain for our country an honor surpassing that won by the discoveries of Newton and Kepler, Herschell and Ross. Can you suggest any way of reaching a consummation so devoutly to be wished?

Very cordially yours

George W. Holley.

President White.