1873-1 Light. 277 



that being a result to him of a mixture of violet and red. The outer ring will 

 appear grey to a red-blind person, and the inner one grey to a violet-blind. 



Microscopy. — A new form of pocket microscope has been contrived by 

 Prof. (j. T. Brown of the Royal Veterinary College. In general construction 

 it somewhat resembles the well-known clinical microscope of Dr. Beale, but is 

 very much smaller, the extreme length being only 3 inches, and packed in its 

 case with two slides and some thin glass measures 3^ inches in length by 

 1 inch wide, and i\ inches in depth. A case double in width will hold, in addition, 

 an extra eye-piece, two objectives in boxes, a glass tube, and two dissecting 

 needles. The short body necessarily involves a loss of magnifying power; 

 this is, however, met by using a very deep eye-piece, the instrument with an 

 E eye-piece giving the same power as an A eye-piece with a 10-inch body. 

 The fine adjustment is made, as in Dr. Beale's instrument, -by sliding the 

 draw-tube containing the eye-piece, a mode of adjustment characterised by its 

 extreme sensitiveness. It is capable of working with powers as high as an im- 

 mersion twelfth. The instrument has been especially designed for observa- 

 tions in veterinary' practice, where it is necessary to have the microscope 

 ready for use at any place : for this purpose it is especially suited, as packed in 

 its case, it is less in dimensions than any case of surgical instruments. It will 

 no doubt prove very useful to field naturalists, and often prevent worthless 

 gatherings being brought home by permitting examinations to be made on the 

 spot. The only disadvantage of the microscope is, that owing to its small 

 size, the objectives and slips of glass are of corresponding dimensions. This 

 prevents the utilisation of the observer's stock of objectives, and also the ex- 

 amination of objects mounted on the usual 3x1 slides. 



At the suggestion of Dr. Pigott, a micrometer scale has been ruled by Mr. 

 Ackland on the flat side of a plano-convex lens of very long focus ; this is in- 

 serted into the diaphragm of the eye-piece. The definition of the object is less 

 impaired than when the old form, having several plane glass surfares, is used. 

 It is also easier 10 make with accuracy, as there is always more or less 

 difficulty in working perfectly true parallel surfaces. It will doubtless 

 prove of equal value for dividing the field of the microscope into a number of 

 squares for the purpose of making drawings, a favourite method with some 

 observers, and to whom better definition than with the original plane disc 

 will be a welcome improvement. 



Some guide to beginners in the use of the micro-spectroscope has long been 

 a desideratum ; this want is likely to be supplied. An introductory work on 

 the subject, with numerous figures of absorption-spectral lithographed by the 

 author, is reported to be in progress. Work in this department has been 

 much hindered by the want of such help, many instruments being almost use- 

 less to their owners for lack of some practical hints as to their employment. 

 The subject is one which has a future before it ; little or nothing is at present 

 understood as to cause of the remarkable phenomena of the absorption- 

 spectrum, and there is plenty of work, with the probability of valuable dis- 

 coveries, for those who apply themselves to such researches. 



Mr. T. Johnston English has brought before the Quekett Microscopical 

 Club a new apparatus for injecting animal tissues for microscopical purposes. 

 The instrument consists of a Woulfe's bottle with three necks. No. 1 is 

 fitted accurately with a cork, through which passes a glass tube about the 

 diameter of a goose-quill, one end of which reaches to the bottom of the 

 bottle, and to the other bent end is tied about 12 inches of india-rubber tubing 

 of the same diameter. The glass tube is made perfectly air-tight in the neck 

 of the bottle by sealing-wax varnish, and the india-rubber one is closed by a 

 pinch-cock. In No. 2 neck is placed a simple contrivance which answers the 

 purpose of a condensing syringe. It consists of a piece of glass tubing 5 or 6 

 inches in length fixed air-tight in the cork ; to its upper extremity is attached 

 a small india-rubber ball, having a small hole in one side, and to the lower 

 end a small oil-silk valve, like those used in air-pumps, opening downwards. 

 The third neck is closed by a cork, and serves to introduce the injecting fluids. 

 To use the instrument, the proper sized nozzle is fixed on the india-rubber 

 vol. in. (n. s.) 2 o 



