TRANSACTIONS OF THE SECTIONS. 7 



were also immersed to serve as conducting plates for the return current. A Smee's 

 battery of two pairs of plates was used, and when the connexion was made with a 

 galvanometer on the opposite bank, a steady deflection of 30° was maintained, and a 

 strong blue mark was produced by a steel electrode on paper moistened with a 

 solution of prussiate of potash in diluted muriatic acid. In this experiment the 

 conducting plates were placed close to the wire, and on opposite sides of it, so that 

 the return current passed diagonally across the exposed wire. The water in this 

 case appeared to act as a conductor and as a non-conductor at the same time, in 

 ■proportion to the surfaces exposed to its influence. Tn the next experiment the wire 

 was doubled, and a current of electricity from the same battery was transmitted 

 through the wires, both being immersed in the water. In this case the deflection 

 of the needle was more prompt, and it continued steady at 45"^. From these ex- 

 periments, which Mr. Bakewell stated were a confirmation of those undertaken by 

 Mr. Bain and Lieut. Wright with a diflferent object in 1841, he inferred that the ex- 

 posure of a large surface, as the electric telegraph wires from post to post, presented 

 greater opportunity for the dispersion of electricity in moist atmospheres, than the 

 points of connexion with the posts, even supposing the wires to be entirely unin- 

 sulated and connected by water with the earth. 



On a New Mode of Illumiiiating Qpake Objects under the highest jiowers of 

 the Miaoscope. By Charles Brooke, M.B., F.R.S. 

 A parallel pencil of rays is obtained by placing a camphine-lamp (which of all 

 kinds of lamps gives the most intense illumination) in the principal focus of a com- 

 bination of two plano-convex lenses. This pencil is received on the surface of a 

 small parabolic mirror, the vertex of which is truncated, so that the focus of the 

 mirror may be about 0-1 inch beyond the truncated edge. Tiie rays which are con- 

 verging to the focus are received 'on the surface of the small plane mirror, which is 

 attached to the bottom of the object-glass, so that the surface of the mirror may be 

 nearly level with the lowest surface of the object-glass. All the rays of light which 

 eubte'ud any angle from that of the object-glass, up to about 170°, are thus rendered 

 available for the illumination of the object, which, as it is illuminated by very oblique 

 rays, must not be placed in a depression or cavity of any kind. 



On a NeiK Arrangement for facilitating the Dissection and Drawing of 

 Objects placed under the Microscope. By Charles Brooke, M.B., F.R.S. 



Two short pieces of tube, one of them the size of the eye-piece, the other the same 

 size as the body of the microscope, are attached at an angle of about 4° to the sides 

 of a brass box containing a rectangular prism. The smaller tube enters the body of 

 the microscope, and the larger receives the eye-piece. The image that enters the eye 

 is now inverted in a plane passing through the axes of the body and of the eye-piece ; 

 and in order to erect the image, a cap is placed over the eye-piece, to which is 

 attached a small rectangular prism, having its axis in the plane in which the image 

 is already inverted. This arrangement provides a very convenient position of the 

 eye, when the hands are engaged in manipulating an object placed under the 

 microscope. 



A rectangular prism has already been introduced into the body of the microscope 

 by Nachez ; but as this was placed near the object-glass, it must to a certain extent 

 interfere with the definition of the object. For the purpose of drawing, a small piece 

 of parallel glass is substituted for the rectangular prism placed in front of the eye- 

 piece, through which the drawing-paper is seen directly through two opposite sur- 

 faces, and the object is seen by reflexion from an outer surface placed at an angle of 

 about 45° with the axis of the" eye-piece. The image inverted by the first reflexion 

 is again inverted in the same plane by the second, and is therefore correctly repre- 

 sented in the drawing. 



On the Progress of Experiments on the Conduction of Heat, undertaken 

 at the Meeting of the British Association at Edinburgh, in 1850. By 

 Professor J. D. Forbes, Sec.R.S.E. 

 After the close of the Edinburgh meeting 1 lost no time in preparing for the pro- 



