Dr Goring on Heflecting Microscopes. 37 



gorian telescope had, I think, been invented previously ; but 

 he, no doubt, saw instantly (as any one else must), how far 

 preferable it would be to cause the cone to be directed to the 

 side of the tube instead, on account of the small size the diago- 

 naLrequired to effect that purpose, and the greater quantity of 

 light it would reflect. Amici reversed Sir I.'s construction, 

 and invented the best reflecting engiscope we shall ever pos- 

 sess, and the only one that has ever come into use. or is able to 

 compete with the refractors now made. Now Sir D. B.'s con- 

 struction for a microscope may evidently be reversed, and con- 

 verted into a telescope of small size for terrestrial objects; and 

 it appears to me that such an instrument will be the best ap- 

 plication of it, or, at any rate, it will be far better in proportion 

 than the microscope. 



Receipt to make a small dumpy Rejlecting Telescope, fur ter- 

 restrial objects, a la Goring — Work a metal of 3 inches aper- 

 ture to a parabolic curve for a focus of 9 inches ; it must have a 

 liole in its centre f ths of an inch in diameter. Then figure a 

 plane one Jth of an inch in diameter, — it might be made larger 

 in the first instance, and then have its bad edges turned off 

 with a diamond tool ; it will also be advisable to turn a shoul- 

 der |th of an inch wide all round this speculum in addition, so 

 as to leave its bright surface only |ths of an inch in diameter 

 (which is all that comes into operation). The shoulder is to be 

 blacked afterwards, that it may form a black circlet, — the 

 image of which, on the visual pencil, is to co-operate with an 

 eyehole in excluding false light. Both metals are then to be 

 fitted up in a tube about 8 inches long, with the same adjust- 

 ments employed in Cassegrain's, as the focus of the instru- 

 ment will be adjusted in the same manner. When the teles- 

 cope is used to view a distant object, the surfaces of the two 

 metals will be 1\ inches distant from each other. In the next 

 place, a slender erecting eye-piece must be made like those used 

 for the smallest spy-glasses, but having its objective part, or that 

 which formsthesecondary image, composedof twodouble cement- 

 ed achromatics in contact, having Jths of an inch of aperture,and 

 Jiboutaninch of solar focus, — onetriple r^jwcTJ^frfachromatic (hke 



