198 



HARDWICKE'S SCIENCE-GOSSIP. 



by the little plane mirror, b, and brought to a focus 

 at d. Eg. 110 shows the arrangement adopted by 

 Mr. Tulley ; the object, c, is magnified by the specu- 

 lum, a, and thrown upon the plane reflector, b, 

 and from this reflector towards the eye-piece. 



These diagrams represent the reflectors about 

 the actual size, and were screwed in or on to the 

 body like the modern objective. 



<7 .,-— 



c^3 



Fig. 109. Reflecting Arrangement of Amici. 



The original dimensions of Araici's Engiscope 

 were as under —Elliptic metal 1 inch aperture, 

 and 2V% inches focus ; diameter of diagonal mirror, 

 i inch ; length of tube, 1 foot. 



Dr. Young also turned his attention to the im- 

 provement of the reflecting microscope. The 

 following is his description of the structure of one 

 of these instruments, or, as they were then called, 

 Engiscopes. 



" Mr. Cuthbert and myself became the parents 

 of the instrument in its most effective form, as 

 follows. Mr. Cuthbert had devoted a very large 

 portion of his time to the making of metals for 

 dumpy Gregorian Telescopes, frequently having 

 an aperture of 3 inches to a focus of only 5 ; he 

 was, therefore, exactly cut out for a maker of 

 Eng'iscopes. I had chanced to be introduced to 

 him when lie had just made a microscopy on 

 Amici's principle, having an aperture of an inch 

 and a half to a focus of three inches, with a body 

 one foot in length. Just about this period I had 

 discovered the properties of the feathers and scales 

 of insects as test-objects ; we tried the instrument 

 with them ; but though the figures of its metals were 

 excellent, we found its performance unsatisfactory. 

 I therefore recommended Mr. Cuthbert to construct 

 a pair of metals of which the concave should be only 

 half an inch focus, and to shorten the body to four 

 or five inches. He accordingly succeeded in making 

 a pair of of an inch focus and "3 of aperture 

 which gave a delightful foretaste of what might, be 

 expected from reflecting engiscopes when perfected. 

 Its body was inserted into the cleft socket of the 

 stand of a small spy-glass, Mr. Cuthbert happened 

 to have by him, and I lent him the stem of a single 

 microscope, made by Samuel Yarley, to attach as a 

 dependent bar to the objective end of the body, 

 which happened to suit it very well, and this ar- 

 rangement constituted the original pattern of the 



instrument I also particularly explained to 



him a method by wh.ch a metai of an unlimited 



angle of aperture might be made to act on trans- 

 parent bodies without increasing the size of the 

 small metal* 



" In relating these anecdotes I am afraid I shall be 

 justly accused of egotism, but I am sure that by- 

 and-by, when the invention shall have obtained 

 a venerable beard of due length, they will be read 

 with pleasure." Dr. Goring and Mr. Pritchard 



m 



Fig. 110. Reflecting Arrangement of Mr. Tulley. 



afterwards made this form of instrument with 

 further improvements, or, as Dr. Goring puts it, 

 " with fiual improvements, which my worthy 

 coadjutor Mr. Pritchard and myself, by clubbing 

 our wise noddles together (as we imagine), effected 

 in it." 



He then proceeds to describe the instrument, 

 beginning with the " foundation," that is to say, the 

 stand or pillar, on which he gives his reasons for 

 preferring a cruciform foot to a triangular one ; at 

 "the same time he admits that, if wanted to fold 

 up together, in order to pack up in small compass, 

 the tripod is the preferable coustructiou, for the 

 cruciform must be made in one piece. Mr. P., 

 of course, makes them to suit the fancy of pur- 

 chasers. I have no doubt he would, to oblige a 

 good customer, mount an instrument on a mop- 

 stick, or the top of an old brass candlestick, as 

 Sir I. Newton did the original of his telescope." 



The manufacture of reflecting microscopes re- 

 ceived a severe check, at least in this country, 

 " Mr. Cuthbert's eyesight having decayed, so that 

 he can only work metals of small angular aperture, 

 and no other artist being- as yet capable of sup- 

 plying his place." The solar focus and angle of 

 aperture of the metals supplied with the rellectiug 

 engiscope were as follows : — 



Solar Focus. 



No.l 



2 

 3 

 4 

 5 

 6 



Angle of 

 Aperture. 



2 inches 13^° 



1 inch ISr 



-frof an inch 274° 



36-r 



4H° 

 55° 



in 



* " Vide my paper in the Quarterly Journal of Science of the 

 Royal Institution, vol. xxi. p. 34, and pi. 1. In this tract 

 will he found the fir-t description ot the aquatic live-box, 

 which like all other good things, is claimed by half a dozen 

 fathers, while a bad thing is sure t,> have only one, or to be 

 i.ke a bastard without any father at all." 



