Page:Hardwicke's Science-Gossip - Volume 1.pdf/253

Photo-micrographs.—In a recent number of the British Journal of Photography, Mr. John Bockett has recently detailed his method for the production of Photo-micrographs by means of an ordinary landscape lens and camera. With regard to the exposure requisite, he says:—"The exuvia of spider, skin of caterpillar, leg of beetle, and the star-fish, were all done in open daylight, through an eighth of an inch stop, in one minute and a quarter."

Microscopic Lamp.—A good microscopic lamp is stated by Dr. Beale to still be a desideratum, and as with high powers, and also binocular microscopes, the importance of having a superabundance of light is imperative, I beg to submit to your readers a description of a lamp which I have had made (and which will be exhibited at the North-Eastern Exhibition at the Agricultural Hall, Islington), answering every purpose. It has been in use quite three years. Its construction is as follows:—A brass circular foot is countersunk into a broad base of mahogany (thereby obtaining stability without adding much to its weight), carrying a main stem. Upon this glides another tube (to the bottom of which is fitted a clamping screw), as also a spring holder to carry a Belmontine lamp. Sliding upon this tube are two pieces of apparatus, one a reflector and the other a condenser; the latter about 2 inches in diameter, the former from 3½ to 4 inches, and of the same or little longer focus than the distance which intervenes between it and the convex side of the plano-convex lens of the condenser. A shade covers the reflecting and refracting apparatus. With regard to its arrangement when in use, it is only necessary after the lamp is lit to move the reflector by slipping it up and down on the auxiliary tube, until the bull's-eye condenser is equably illuminated, which can easily be seen by placing a small disc of white card upon the plane surface of the condenser. If the whole has been arranged for transparent objects as above, and it is required to be used to show opaque objects, the auxiliary tube has only to be raised, and the arrangement previously alluded to still remains intact, the said alteration not being attended with the least trouble. It burns Belmontine, which I find far preferable to parafine, being without any smell, and, as I think, with all due deference to Mr. Hall's late deductions, equal to it in light. By its aid I can in my binocular use a ¼-inch bull's-eye piece most advantageously. The light with the lower powers is so intense that a ground or neutral tint glass slide must be used.—John Bockett.

Circulating Cabinet of Objects.—About six months ago some microscopists in Oldham and its neighbourhood formed a circulating cabinet of objects. Not knowing that there is anything of the sort in other towns, I will endeavour to describe it. In the first place we have as many trays as there are members, upon which each member puts six objects, in a horizontal position, held down by an elastic band. To prevent one tray from touching the objects on another, a bead runs all round each, about a quarter of an inch deep: the whole are enclosed in a box made for the purpose. Each member changes the objects on his own tray every time the cabinet comes round to him, and he retains it one week to examine the objects on the other trays. A small memorandum-book, in which are written a few short rules, the remaining space being left for remarks and suggestions, together with a stamp-case, to receive the contributions of the members, which goes along with the cabinet. The expenses of carriage, &c., are taken out of this stamp-case. We find this arrangement to work very well, and have not had an object broken yet.—John Bullerworth.

Pollen.—Your correspondent "E. G. M." directs the attention of your readers to the pollen of the Œnothera, or Evening Primrose. I have seen the pollen of Œnothera offered for sale by dealers in microscopic objects, and have mounted several slides of it for my own use and for exchange with friends. I think the most beautiful pollen-grains are those of the common Marsh Mallow, or of the Garden Mallow, either of which may be had in great abundance. They are superior to the Passion-flower, Hollyhock, Dahlia, or Evening Primrose. Indeed, I know of no pollen worthy of comparison with them.—T. P. Barkas.

Cilia on Diatomaceæ.—A few days ago, while examining a recent gathering of fresh-water Diatomaceæ, I had my attention arrested by peculiar motions near a frustule of Nitzschia sigmoidea. The frustule itself was perfectly stationary, but it was surrounded by a considerable quantity of gritty matter, which was in motion. I observed closely, to see if any animalcules or small diatoms were present, and could not recognize any within the field of the microscope. The matter surrounding the Nitzschia was broken up into small patches and fragments, and the phenomenon that presented itself was the rapid motion of single and accumulated particles of foreign matter down the sides of the Nitzschia, which was lying perpendicularly to the line of vision. The notions were along the sides of the diatom, and all downwards. That direction of motion could not be caused by mere gravitation of the particles, because, as an erector was not used, the apparently downward motion would be in reality upward, and upward motion, under the circumstances, and to such an extent, could only, as it appears to me, be accomplished by the action of cilia flashing in one direction. Endosmose and Exosmose, or any other proposed theory to account for the movements of Diatomaceæ, will not explain the motions of the ree particles as above described—T. P. Barkas.