32 



SCIENCE-GOSSIP. 



[Feb. 1, 1866. 



siderable quantities in the tissues of many tunicate, 

 both simple and compound. They explained this by 

 supposing it might be dissolved by the gastric juices 

 from the diatoms and many minute vegetable or- 

 ganisms found in the stomachs of the Ascidians, and, 

 being thus dissolved, was then absorbed into the 

 tissues. 



Thus, as Professor Forbes remarks, if the presence 

 of cellulose in the tunics of the Ascidian mollusks 

 cannot be taken as an evidence of an approach to a 

 vegetable nature in these bodies, it affords us at 

 least a wholesome warning against the placing of 

 confidence in asserted chemical distinctions between 

 the great kingdoms of nature. 



P. S. B. 



THE NEW ILLUMINATORS FOP HIGH 

 POWERS. 



THE principle of reflection has been made use of 

 in optical instruments for a variety of purposes, 

 and recently that employed in the transit instru- 

 ment has been modified and brought to bear upon 

 the microscope in a very remarkable manner. The 



instruments alluded to, 

 are the new patent il- 

 luminators of Messrs. 

 Powell and Lealand ; 

 Smith, Beck, & Beck ; 

 and a reflector by 

 Messrs. Ross of Lon- 

 don, and Dancer of 

 Manchester; which lat- 

 ter has also adapted a 

 small speculum answer- 

 ing the same purpose. 

 That of the first-named 

 firm consists of a 

 tube of brass, fitted 

 at one end with a 

 moveable male and 

 at the other a female 

 screw, thereby en- 

 abling it to be 

 screwed into the 

 body of the instru- 

 ment, and an objec- 

 tive into the lower 

 opening. Midway 

 between their two 

 orifices is situated a 



Fig. 25. 



Fig. 26. Powell & Lealancl's 

 Patent Illuminator for Minute 

 Opaque Objects. 



small plate of parallel glass, which receives light from 

 a lamp through a small hole drilled in the side of the 

 before-mentioned tube ; the hole is fitted witli a 

 small diaphragm plate, perforated with four openings 

 of different sizes. The action of the new apparatus 

 consists in transmitting, by means of the plate of 

 glass, the light (received through the side orifice) 



from a lamp through the object-glass down upon 

 and illuminating the object, the rays therefrom 

 passing upwards through the objective again, and 

 impinging upon the field-glass of the eyepiece as 

 usual. The illuminator by Smith, Beck, & Beck 

 is in substance the same, but more simply carried 

 out. The tube for screwing into the microscope, 

 and the orifice thereof for the objective, is lighter 

 than that just described, the moveable upper portion 

 which screws into the microscope being evenly 

 burnished in, to enable the hole, through which the 

 light from a lamp is to be thrown, to be always 

 brought round to the left hand. In lieu of a plate 

 of glass for the necessary reflection, a round disc of 

 ordinary thin microscopic glass is used, the same 

 being fixed by means of shellac into a small pin, the 

 pin and disc gliding centrally into position through 

 a slot cut in the tube. The pin projects, terminat- 

 ing in a small milled head, whereby the best angle 

 of reflection can be obtained ; this will be found to 

 be 45°. The next method consists in making use 

 of the left-hand tube of the binocular microscope, 

 which is fitted with a piece of tube carrying a 

 mirror, the light being by its means reflected on to, 

 and through the prism, and so through the object- 

 glass, the right tube conveying the magnified image 

 of the object to the eye of the observers. The specu- 

 lum last referred to fits into the body of the micro- 

 scope just above the objective, and, reflecting a small 

 portion of the rays, acts similarly to the illuminators 

 first named. 



After the above description of the apparatus, the 

 next point to be considered is the illumination ; and, 

 indeed, upon the management of this, nearly the 

 satisfactory working of the whole depends. My 

 remarks now will be confined to the two illumi- 

 nators first mentioned. Too much light carries 

 flare, and the object appears foggy and indistinct. 

 The best method I have found, is to use the small 

 condensing lens fitted into the stand (not the stage) 

 of the instrument, the lamp being raised to the 

 height necessary to illuminate the whole of the lens. 

 The circle of light transmitted by the condenser 

 should just fill the aperture of the small diaphragm 

 one size larger than intended to be used. With the 

 instrument by Smith, Beck, & Beck the same object- 

 can partially be obtained by moving the lamp a 

 little further away, or on one side. Another great 

 improvement (with some objects) I find, can be 

 made by causing the light to pass through a plate 

 of thin neutral-tint glass, the flare, if not excessive, 

 being entirely absorbed. We next arrive at the 

 class of objects to which this description of illumi- 

 nator is specially adapted ; these will be found to 

 consist of scales, say Papilio Paris, Azure Blue, thin 

 sections of wood, &c, or, in fact, anything which is 

 tolerably flat. With respect to objects covered with 

 glass, no matter how thin, the illuminators will not 

 work, the reflection from the glass-cover enveloping 



