HARDWICKE'S SCIENCE-GOSSIP. 



65 



or well mounted the objects, the result with imperfect 

 or unsuitable illumination must be unsatisfactory. It 

 was a fact that illumination was very generally a 

 weak point of microscopists ; the inference being 

 either that they were unacquainted with its principles 

 or failed in their practical application. He then 

 proceeded to explain and illustrate by means of 

 diagrams the laws of reflection, refraction, total 

 reflection, &c, so far as they applied to the subject. 

 He next passed in review the various sources of light, 

 of which a bright white cloud is generally said to be 

 the best, but unfortunately it is not often available, 

 especially as the bulk of microscopists must neces- 

 sarily work only at night. Next to this, in point of 

 purity, comes the electric light, but though it has 

 been used with a certain amount of success it can 

 never be much used on account of its cost and trouble, 

 and the same applies to the oxy-hydrogen and oxy- 

 calcium lights. Ordinary microscope lamps then 

 are practically the best, and of these there are 

 various descriptions, some very elaborate and costly, 

 but it is doubtful if they are worth (except, perhaps, 

 for very special purposes) their extra cost, and if as 

 good results cannot generally be obtained with the 

 less expensive ones properly managed. He then 

 Teferred to the various modes of illuminating objects 

 by transmitted light, urging the neces>ity of so 

 arranging the lamp, bull's-eye, &c, as to ensure the 

 rays of light passing to the microscope parallel to its 

 axis. This being the light usually required not only 

 for ordinary transparent objects, but also for polari- 

 scope dark ground appliances, &c, he expressed a 

 •strong opinion as to the advantage of using the 

 light direct from the lamp, without the intervention of 

 a mirror, and described a simple plan adapted by 

 himself whereby the microscope, lamp, &c, having 

 been once satisfactorily placed, could after removal 

 be quickly replaced in exactly the same positions, 

 thereby effecting a very considerable saving of time, 

 less than one minute being required for the whole 

 operation, from lighting the lamp to beginning to 

 observe. After describing various modes of 

 illuminating opaque objects, he concluded by urging 

 all microscopists who had not yet done so to make 

 themselves thoroughly acquainted with the con- 

 struction of the microscope and its various accessories, 

 so as to understand each part, its use and mode of 

 action, for with this knowledge and by the intelligent 

 application of the optical laws involved, they would 

 be able readily and certainly to obtain results which 

 otherwise would only be got by chance, if at all. 



Mounting Insects. — In reply to a query of 

 T. R. Brokenshire : — The best cell I have seen, or 

 used for mounting insects whole, without pressure, is 

 a metal cell with four equidistant projections. It 

 was lately figured and described in the Journal of the 

 Royal Microscopical Society. The projections on 

 the cell are to support the cover glass, and the spaces 



between the projections allow the'balsam or other 

 medium, in which the object is mounted to harden. 

 The cell is admirably adapted f'ir the purpose for 

 which it is intended, and is certainly a most ingenious 

 arrangement. Mr. George Wilks, of Weaste, near 

 Manchester, is the inventor ; and doubtless a note 

 dropped to him would bring far more information 

 about the invention, and how to use it, &c, than I 

 can give the inquirer. — E. B. L. Brayley. 



Mounting Insects. — Replying to the query 

 respecting mounting insects, &c, I beg to call 

 attention to a paragraph on page 477 of the " Royal 

 Microscopical Journal " for 1S84. Mr. George Wilks, 

 Salford, suggests a new cell for mounting without 

 pressure in Canada balsam. The cell is made of 

 soft metal, and has four elevations alternating with 

 depressions, the cover glass resting on the upper 

 points of the curves. By leaving an excess of balsam 

 round the cell and cover glass, air bubbles ultimately 

 escape through the spaces, and loss by evaporation 

 or essential oil in the balsam is provided for. If the 

 cell is too deep for the object, it can be pressed 

 between two glass-slips until shallow enough. The 

 utility of this cell has been successfully demonstrated, 

 by Mr. John W. Miles, before the mounting sections 

 of the Manchester Microscopical Society. — IV. S. 



Diatom Structure. — In a letter on diatom 

 structure, which appears in the " English Mechanic " 

 for February 6th, Dr. Wallich gives reasons for 

 agreeing with Dr. Flogel "that in such genera as 

 triceratum and coscinodiscus, the little hexagonal or 

 cylindrical cavities, though completely closed by a 

 silicious film on the internal surface of a valve, are 

 not closed by any such membrane on the outer 

 surface of the valve." 



Life Histories of little-known Acari. — 

 Mr. A. D. Michael, who has distinguished himself by 

 his researches in this difficult and little known group, 

 recently read a paper on the Tyroglyphidae before 

 the Royal Microscopical Society. In 1873, Riley 

 published a report on the ravages of the apple-bark 

 louse {Aspidotus cotuhiformis), and described an 

 acarus which was supposed to destroy that pest, and 

 which he thought might be the Acarus mains of 

 Shinier. Riley only describes the female. Mr. 

 Michael has found the acarus in England, under the 

 bark of reeds, destroying the reeds, not feeding on 

 any insect, and concludes that it is probably a feeder 

 on various kinds of bark, not on animal life ; he has 

 traced the whole life-history. The male (previously 

 unknown) presents the exceptional features possessed 

 by the male of Tyroglyphus carpis, discovered by 

 Kramer in 1 881, and the hypopial nymph has been 

 figured by Canestrini and Fanzago in 1877, under the 

 name of " parasite of an Oribata," but without 

 explanation. Mr. Michael finds in the life-history of 

 this hypopus a confirmation of his views that the 



