070 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
motion focussing screw, the milled head of which is seen at the lowest 
point of its support, immediately in front of the tail-piece. This sup- 
port of the substage swings in arc (the reflection of a portion of the arc 
can be seen in the mirror), llie centre of rotation being the object on the 
stage. The substage, carrying the condenser, can also be further turned 
obliquely to the optic axis by means of the pivot in its front support. 
By means of these two motions extreme obliquity of illumination can be 
obtained. 
“ With regard to the invention of the swinging substage, there is one 
figured in Adams on the Microscope, 1798 (PI. 9, fig. 5), in connection 
with Jones’s Lucernal Microscope, as improved by the Rev. John Prince, 
of Massachusetts, and Mr. John Hill, of Norfolk.* * * § The idea underlying 
this construction was not for purposes of oblique illumination, as we 
now understand it, i. e. for sending an oblique beam below the stage on 
a transparent object, because this kind of illumination would be simply 
useless with a lucernal Microscope which projected’ the image on a 
ground-glass screen. But the swing was applied in order that the sub- 
stage might be turned round to the upper side of the stage, so that it 
might become a super-stage illuminator for opaque objects. Substage 
oblique illumination was neither intended nor used at this date. The 
next time we meet with a swinging substage is in Grubb’s Sector Micro- 
scope | (described before the Royal Irish Academy on May 10th, 1852, 
and patented 1854). Jn this Microscope the substage, with a right- 
angled prism attached beneath it, was fixed to a slot, which traversed in 
a radial groove. J Coming to more recent times (1871), Tolies, § in 
America, revived the swinging substage, to facilitate the resolution of 
lined tests with oblique light. He was followed by Bulloch || (1873) 
and Zentmayer^T (1876) in America, as well as by all the principal 
makers in this country, Powell excepted. This absurd craze culminated 
in the Ross-Wenham radial Microscope of 1882.** I am, however, 
happy to say that the 3/4 axial cone has slain the Lernaean Hydra, and 
both swinging substages and radial Microscopes have sunk to rise no 
more. Returning, however, to the model before us, we have a very 
perfect and early form of swinging substage ; for I first saw this Micro- 
scope in 1870, and at that time it must have been about ten or fifteen 
years old. Several of the objectives used with this Microscope were 
computed and made by its designer.” 
* Journ. R.M.S., vol. vii. ser. 2, 1S87, p. 297, fig. 45. 
f Op. cit., vol. iii. 1880, p. 1056, fig. 126, and Proc. R. Irish Acad., v. (1853) p. 296. 
X The following is abstracted from a footnote which occurs in a paper on ‘ The 
Measurement of Aperture,’ written by the learned and Reverend J. R. Robinson, 
D.D , Dean of Armagh, with reference to a new Microscope Mr. Grubb had made for 
him (Quarterly Journal of Microscopical Science, iii. p. 166, 1855). 
“This Microscope ( Grubb's Sector ) deserves to be known. . . . Mr. Grubb’s 
illuminator is a prism whose aberrations are corrected for a lamp placed at a given 
distance in the plane of the stage. It travels on a graduated arc of 120°, and through 
this range its focus continues on the object. . . If raised above the stage it gives at 
once a capital illumination for opaque objects; it acts well with Lieberkuhn and 
Nicol’s prism, and trifling additions make it equally effective with Mr. Bergin’s 
parallel illuminator, which shows some objects with peculiar distinctness.” Mr. 
Bergin’s illuminator was a combination of a rhombic prism with Mr. Shadbolt’s 
parabolic reflector. 
§ Journ. R.M.S., vol. iii, 1880, p. 1061, figs. 128, 129. 
|| Tom. cit., 1880, p. 1068, fig. 133. ^ Op. cit., vol. ii. 1879, p. 320, and 2 figs. 
** Op. cit., vol. ii. ser. 2, 1882, p. 256, 4 figs, and pi. p. 145. 
