HARDWICKE'S SCIENCE-GOSSIP. 



2G9 



Surely, there must be residing in this part of the 

 couuty a few naturalists, botanists, and lovers of 

 nature generally who would be willing to join to- 

 gether and form a Society, having for its object the 

 study of the fauna and flora of one of the most in- 

 teresting, and, for its size, least known districts in 

 England. 1 would most willingly co-operate and 

 assist in the formation of such a society, and I shall 

 be glad to have the views of any persons interested 

 in the subject, either through the medium of this 

 journal or by letter. 



Erockenhirst. E. D. Marquand. 



E. II. WENHAM'S NEWEST BINOCULAR 



ARRANGEMENT FOR THE HIGHEST 



POWERS. 



A 



S that excellent binocular arrangement for low 

 powers devised by Mr. Wenham in 1S60, 

 and which has not yet been superseded by a better 

 one, yields only a well-illuminated field with objec- 

 tives of no shorter focus than the half-inch of 40° 

 angular aperture, owing to the shortness of the 

 focii of high powers, great efforts have been made 

 in devising and perfecting binocular arrangements 

 suitable for the highest powers of the microscope. 

 Stephenson's stereoscopic binocular, Powell & 

 Lealand's patent non-stereoscopic, and several 

 stereoscopic and non-stereoscopic binocular ar- 

 rangements of F. H. Wenham and others, most of 

 them requiring special bodies, have been devised, 

 and have given more or less satisfaction. 



Messrs. Ross & Co., London, supplied me in 

 August last with a new binocular arrangement for 

 the highest powers, which I have used since then ; 

 and as this is the first of its kind made, and as I 

 cannot speak of it but in terms of unqualified 

 praise, I beg to call the attention of all those en- 

 gaged in prolonged observations under high and the 

 highest powers to this ingenious invention. It 

 appears that this new arrangement was devised by 

 Mr. Wenham some years ago, but the apparent 

 difficulties of making it delayed its being carried 

 out earlier. This high-power binocular arrange- 

 ment consists of two small superposed prisms of 

 crown glass, fastened into a frame which fits in the 

 place of the Wenham prism, for which it can be 

 instantly exchanged. Through the courtesy of 

 Mr. Wenham, who made this first prism himself, I 

 am enabled to give a diagram of it. The larger 

 prism (A) resembles in form and size the well- 

 known Wenham binocular prism. The angle formed 

 by the lower horizontal surface and the plane p is 

 40°, which is beyond the limit of total reflection, 

 consequently a ray passing into the prism {A) is 

 only partly reflected ; but to enable the transmitted 

 part of the ray to pass into the eyepiece, another 



r prism (B), having also an angle of 40°, is placed 

 above A, which renders the upper and the lower 

 surfaces parallel to each other. The transmitted 

 part of the ray now passes straight through the 

 two prisms, as if simply a piece of plate-glass was 

 interposed. The remaining part of the ray from 

 the object-glass is intercepted by the two inclined 

 surfaces, which have as much obliquity as can be 

 given for transmission, and the amount of light 

 reflected by the combined surfaces is consequently 

 nearly equal to that transmitted, and, on account of 



Fig. 159. Diagram of F. H. Wenham's newest high-power 

 binocular Prisms, with angles, for Ross & Co's microscope. 



their proximity, the reflected images of the two 

 surfaces are combined as one. This reflected image 

 is finally reflected up the inclined body from the 

 plane q, just the same as in the low-power binocu- 

 lar ; but as it is not possible to arrange this last 

 surface within the range of total reflection, it re- 

 quires to be silvered. 



This arrangement acts non-stereoscopically, i.e., 

 it reflects identical images into both oculars; and 

 its chief advantage consists in the relief it affords 

 to both eyes. This, however, is a most important 

 point when prolonged investigations are to be made 

 as, for example, such marvellous researches in the 

 life history of the lowest forms of animal life as 

 were made by the Rev. W. H. Dallinger,V.P.R.M.S., 

 and Dr. Drysdale, which extended without inter- 

 ruption for months, and which to a large extent 

 overturned the theory of spontaneous generation, 

 would probably never have been made but for 



