﻿130 M.S. Merz on a small Universal Stellar Spectroscope. 



words, of two spectroscopes, each of which may be used singly, 

 and which are in part complementary to each other. The one 

 part, which is a simple direct-vision spectroscope, is provided with 

 a prism of novel construction. This prism consists of five ele- 

 ments, two of which are of flint glass, each having a refracting- 

 angle of 84°; the other three prisms are of crown glass; one of 

 them has also a refracting-angle of 84°, the other two of 87°, as 

 shown in Plate II. fig. 4. 



This portion of the apparatus is furnished with a positive eye- 

 piece with an equivalent focal length of 1 inch, and it is also 

 provided with a cylindrical lens of 1 inch radius. The arrange- 

 ment of this portion of the apparatus is shown in fig. 1 . 



The compound spectroscope, which is represented in fig. 2, is 

 provided with a similar spectral prism. It has a tube furnished 

 with a slit, and a collimator, and likewise an observing-telescope. 

 The object-glasses of the latter and of the collimator are of the 

 same focal length, namely 4 inches; their aperture is § of an inch. 



The observing-telescope carries, moreover, a needle-micrometer 

 with an eyepiece of J-inch focal length. It is also provided 

 with two red sun -glasses, which admit of being used either singly 

 or together. This compound spectroscope is moreover furnished 

 with a small divided position -circle situated at B. 



The spectral prism can be unscrewed from the simple appa- 

 ratus (fig. 1) and inserted at A, between the observing-telescope 

 and the spectral prism of the compound apparatus (fig. 2), 

 whereby the dispersion of the spectroscope is doubled, and the 

 entire instrument rendered available for the observation of the 

 solar protuberances. 



With the view of such observations, a peculiar construction has 

 been given to the slit (fig. 3), by means of which, through the 

 medium of a screw, its two steel jaws can be simultaneously 

 moved away from the centre and opened to the distance of nearly 

 a quarter of an inch. The slit is further fitted with an arrange- 

 ment for throwing aside the illuminating prism that is employed 

 in comparing the spectra of flames. This latter movement is 

 effected by means of a small lever, to the long arm of which the 

 prism in question is attached, and the short arm of which is in- 

 serted into an aperture in the rotating ring R. When such a 

 motion has been given to this ring that the aperture at which 

 the light enters (a) is closed, the prism no longer remains oppo- 

 site the slit, so that the cone of rays derived from the refractor 

 has then free passage through the full width of the jaws. 



The lateral movement near K on the observing-telescope 

 enables any separate colour of the spectrum to be brought into 

 position, while a similar movement at K' near the slit serves for 

 altering the angle of incidence of the rays, thus bringing into 



