418 



Progress in Science. 



[J"iy, 



Fig. 12. 



A 



dinary ones are used, the ordinary being shut off; as there is a good deal 

 of colour in these rays, it is neutralised by the double wedge flint-glass prism, 

 of angle of 25 , b, placed over the double-image prisms, which also causes the 

 rays to cross, the separated rays, c' c, then proceed to 

 two symmetrically divergent tubes containing the eye- 

 pieces. The tube containing the prisms and eye-pieces 

 fits into the single body in the place of an ordinary 

 draw-tube. The inventor states that the instrument 

 answers well as a micro-polariscope, as the double- 

 image prism takes the place of the analyser, and 

 with much better effect than the usual Nicol prism, 

 as it is worked with greater truth, but only one body 

 can be used at a time unless there is a Nicol prism in 

 one of the tubes, otherwise there will not be the same 

 colour in each field. Mr. Ahrens also suggests that 

 this binocular eye-piece might be used with advantage 

 in the telescope, for by its means we could tell whether 

 the object examined shone by its own or by reflected 

 light. 



Mr. B. T. Lowne, M.R.C.S., in describing the 

 structure of the so-called " suckers" on the foot of the 

 male Dytiscus, demonstrates that the production of a 

 vacuum, as commonly supposed, has nothing whatever 

 j|'*^ — ^ — 1 — >— — ^ to do with their adhesion. Upon causing the insect to 



\ / attach itself to the interior of an air-pump receiver, the 



\ / " suckers" did not relax their hold upon the exhaustion 



P m \ / m °^ t ^ ie vesse ^» but the adhesion was rendered closer by 



Hj^NUffl the exudation of the glutinous fluid, which is the real 



pUf^H cause of attachment. In cases where the glue has 



Bail ^j^ffim 1 hardened, the suckers are frequently torn away by the 



insect in its efforts to regain its liberty. 

 Prof. A. M. Edwards has examined a specimen of marble obtained near Thur- 

 man, about twenty-five miles from Saratoga, New York. The whole mass was 

 found to consist oiEozoon Canadense. The material is said to occur in large 

 quantities. The discovery is of great geologicial importance, as it indicates 

 that the rocks belong to the Laurentian period, and the more so as the Cana- 

 dian Geological Survey have only lately traced these rocks into New England 

 — as far, at least, as Salem, Massachusets. Specimens of Eoz'oon, prepared 

 by Dr. Carpenter, are in the cabinet of the Royal Microscopical Society. 



Mr. Charles Cubitt, C.E., in the May number of the "Monthly Microscopical 

 Journal," gives a statement of his views respecting the delineation of objects 

 under microscopic observation. After criticising the drawings of several 

 microscopical observers, which he refers to, and in which he detects various 

 inconsistencies, he gives his own mode of proceeding, which is to make rough 

 drawings of the object, then with the eye-piece micrometer to make all neces- 

 sary measurements. From these data plans and elevations are prepared, and the 

 perspective figure obtained by the process of linear projection well known to 

 mechanical draftsmen. He selects as a subject for practical illustration the 

 familiar Melicerta ringens, and in the plates accompanying his paper gives the 

 plans and sections and the various lines needed in obtaining his finished re- 

 presentation, which is a marvel of patient application and decidedly accurate, 

 but has, nevertheless, an inartistic stiffness. The process seems far too com- 

 plicated and tedious for microscopists in general, and only attainable by those 

 who have studied mechanical drawing in an engineer's or architect's office. 

 The whole paper is written from a decidedly engineering point of view, but 

 will do good in causing greater attention to be paid to accurate representation, 

 although few besides its author have time or skill to carry out his views in their 

 integrity. 



Mr. H. J. Slack, F.G.S.,* gives an account of the "Optical Appearances of 



* Royal Microscopical Society, April 5, 1871. 



