THE QUARTERLY 



JOURNAL OF SCIENCE. 



OCTOBER, 1869. 



I. ON THE SPECTRAL PHENOMENA OF OPALS. 



By "William Crookes, F.R.S., &c. 



A FEW months ago* the writer described a new form of spectrum 

 microscope, in which some of the disadvantages possessed by the 

 old form are removed. The new S|:K3ctriim apparatus consists of 

 two parts, which are readily attached to an ordinary single or 

 binocular microscope, and when attached they can be thrown in or 

 out of adjustment by a touch of the finger, and may readily be used 

 in conjunction with the polariscope or dichroscope ; object-glasses of 

 high or low power can be used, although the appearances are more 

 striking with a power of ^-inch focus or longer ; and an object as 

 small as a single corpuscle of blood can be examined, and its spectrum 

 observed. 



The two additions to the microscope consist of the substage 

 with slit, &c., and the prisms in their box. The substage is of the 

 ordinary construction, with screw adjustment for centering, and 

 rackwork for bringing it nearer to or withdrawing it from the 

 stage. In the accompanying engraving, a b is a plate of brass 

 sliding in grooves attached to the lower part of the substage ; it 

 carries an adjustable slit c, a circular aperture d, • 6 inch diameter, 

 and an aperture o, §■ inch square. A spring top enables either the 

 slit or one of the apertures to be brought into the centre of the 

 field, without moving the eye from the eye-piece. Screw adjust- 

 ments enable the slit to be widened or narrowed at will, and 

 also varied in length. At the upper part of the substage is a 

 screw of the standard size, into which an object-glass, shown at 

 E, of high power, is fitted. The sht c and this object-glass k 

 are about 2 inches apart, and if light is reflected by means of the 

 mirror along the axis of the mstrument, it is evident that the object- 

 glass E will form a small image of the slit c, about • 3 inch in 

 front of it. A milled head f moves the whole substage up or down 



* ' rroceedings of the Royal Society,' May 27, ISfif). 

 VOL. VI. 2 L 



