312 SUMMARY OF CURRENT RESEARCHES RELATING TO 



convex lens and the back of the stage, thus inclosing the mirror and 

 allowing it room to be focused properly when the lid of the box is 

 removed. It is also advisable to fit a sheet of pasteboard P tightly 

 over the body-tube at right angles to it, in order to cut oflf the rays 

 which escape around the object illuminated, pass along the axis of 

 vision outside of the tube, and tend to blur the image on the 

 screen. 



*' Physiological, histological, pathological, and botanical specimens 

 may be clearly shown. A number of students can look on at once. 

 The slides are rapidly changed, and student and instructor may 

 always be sure that they are discussing the same particular cell ; 

 which, unfortunately, is not the case when a beginner in the use of 

 the Microscope looks through the instrument alone. The apparatus 

 may readily be constructed by any one for about five dollars ; it is 

 easily portable, and always ready for use in any darkened room. . . 

 With some lenses, the use of the eye-piece adds distinctness, but in 

 most cases it cuts out too much light. An Abbe illuminator may be 

 inserted. The image on the screen G is seen most distinctly upon 

 the farther side ; and some objects become clearer if the screen be 

 moistened with water, or covered with a thin coat of transparent 

 varnish laid over the ground surface. The image may also be 

 received upon white glazed paper, but this is less clear. 



For demonstration on a larger scale, an oxyhydrogen light can of 

 course be used, or some form of electric light. The arc light is not 

 sufl&ciently steady, and the incandescent light requires a great deal of 

 storage-room for batteries. The light above described shines with 

 thirty -six candle power, is clear and steady, and serves every ordinary 

 purpose : the circulation in the frog's foot, varieties of epithelium, 

 injected lung tissue, tubercle, plant-cells, &c., may all be clearly 

 shown. The colours of stained or injected specimens come out 

 distinctly. 



The principle of this apparatus is by no means new ; but its 

 application is made so easily within the reach of any one who owns a 

 Microscope, that it is especially recommended to instructors in schools 

 and colleges." 



Apparatus for Botanical Lectures.* — Dr. E. Hallier describes 

 the apparatus which he has found useful in his botanical lectures. 



1. Stand for the Magnifiers and Objects. — Whilst it is, of course, 

 always required that each student should have in his hand a perfect 

 example of the plant to be described, and that he should dissect it with 

 the knife during the lecture, and then examine each part separately 

 with the magnifier, yet this is not satisfactory with a large number of 

 students, because the teacher cannot superintend the manipulation of 

 each one separately, and cannot be certain that the specimen is dissected 

 and examined as it should be in order to show its essential parts. 



Accordingly, Dr. Hallier uses the apparatus shown in fig. 63. 

 A is the stand for the magnifier. To the heavy brass foot / the 

 column s is screwed, with an arm a clamped by the screw h, and 



* ^eitschr. f. Instrumentenkuude, i. (1881) pp. 393-7 (1 fig.)- 



