ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



155 



the glass on four pegs S, and is kept in position by the square springs E, 

 for the passage of which two sections A of the frame E are removed. 

 Eunning from the left section A directly inwards as far as the central 

 aperture is a groove V, 1 mm. deep, on the under surface of the glass plate 

 P. In this groove works a short guide-pin X, connected with the end of 

 the left rectangular spring E. When pressure is made on the handle B 



Fig. 24. 



the carrier is moved to and fro along the groove, or in arcs of which X 

 forms the centre, or in a combination of the two movements. As the figs, 

 show, a finder can be employed. 



The apparatus admits of some modifications, such as having the upper 

 surface of the glass plate grooved instead of the lower. 



(7) Miscellaneous Blatters. 



The New Glass.* — In an article widely copied by the American daily 

 press from the ' St. Louis Dispatch ' occur some rather startling statements 

 concerning the discoveries of " Prof. Abbey " and " Dr. Scott," of which 

 the following is a very brief extract. 



" That a recent wonderful discovery in microscopy has not been even 

 noted in the public press may be cited as proof of the general apathetic 

 tendency as regards scientific matters. The Microscope has always been 

 regarded as a wonderful instrument, but by the discovery of an entire new 

 kind of glass lately, its powers are increased to an incredible degree. . . . 

 With the old glass the full power of the Microscope was the discernment 

 of the one-five-hundred thousandth part of an inch, and with the new 

 glass it is claimed that the one-two-hundred-and-four-million-seven-hun- 

 dred thousandth part of an inch can be distinguished. This certainly 

 seems incredible, but positive assurance of its truth is given by parties 

 who have tested Prof. Abbey's and Dr. Scott's new instrument." 



Errors of observation in reading divided instruments.t — Herr H. F. 

 Dorst has endeavoured to compare the relative accuracy of the three 

 methods by which fractions of the divisions on graduated instruments 

 are determined in making measurements ; these are (1) direct estimation, 

 (2) measurement by vernier, (B) measurement with micrometer Microscopes, 

 and the errors corresponding to them may be called respectively estima- 

 tion-, coincidence-, and adjustment-errors. 



To compare these the author made a large number of observations with 

 the naked eye upon various instruments and with sets of lines ruled upon 

 paper, having previously determined that his eye could be regarded as one 

 of normal accuracy and sensitiveness. The observations were made with 

 the graduations both in horizontal and vertical positions, and the probable 



* Micr. Bulletin (Queen's), iii. (1886) pp. 35-6. 

 t Zeitschr. f. Instrumeutenk., vi. (1886) pp. 383-7. 



