The Stanhoscope
Until within the last few weeks I have been unable to obtain a lens sufficiently powerful to be useful and sufficiently portable to be convenient, in examining diatoms on the spots where they .were gathered. I have tried compound microscopes, and found their arrangements on the open field or on the seashore tedious and awkward. I have used the ordinary Stanhope and triplet lenses, but none of them gave satisfaction ; the latter being- much too low in magnifying power to enable me to determine with any certainty what species or even genera I had gathered.
The Stanhoscope, however, is excellently adapted for field purposes, its power is great, ranging from 100 to 150 diameters, its field is clear, and the method of using it is simplicity itself, all that is required being to place the object to be examined, say diatomacæ, desmidese, scales from moths’ wings, &c., ON the square end of the lens, and then look through the apparatus towards the light. The size of the entire apparatus is only one inch in length and five eighths of an inch in diameter ; it is therefore exceedingly portable, and is also very cheap. The lens is of French manufacture, and may be had of any optician who deals in foreign goods, or of any respectable toy dealer for 15. Qd. ; it can also, without fear of injury, be sent post free to any address on payment of eighteen postage stamps.
These Stanhoscopes of French manufacture, being originally made as toy microscopes, and very cheap, are, of course, not in every instance so perfect optically as is desirable ; one half of those sold are very good, but the remainder are either imperfect or very inferior. In order that the public might be supplied with really good articles, at not too high a price, I wrote to a London optician, requesting him to turn his attention to the subject of manufacturing a portable article on the French principle, but with care as to optical details. He, in reply, stated that a small pocket lens of the kind referred to could be manufactured, upon the working of which reliance might be placed, and which would answer every purpose required by a microscopist in search for diatomaceæ, desmidese, or infusoria, but that the price could not be less than five shillings.
As a proof of the power and clearness of the better Stan- hoscopes of French manufacture, I may state that I can recognise with ease Nitzschia closterium, N. reversa, and even Cocconeis excéntrica, when they have been prepared and the cndochrome has been removed by acid.—T. P. BARRAS, New- castle-on-Tyne.
On the Improvement of the Compound Microscope
—You would much oblige me by the insertion of the following remarks on the improvement of the Compound Microscope, as sequel to a contribution of July, 1863, to which I must refer your readers. Concave mirrors in place of lenses in the eye-piece, so inclined as to reflect the body of rays into the form of a figure of 4, would afford a convenience of manipulation almost irrespective of the dimensions of the instrument. If approved, a mirror as objective also might afford additional mechanical facilities. On a smaller scale the form of the letter N might be preferred. Attached to each objective should be a length of tube twice or more its focal distance. To avoid moving the body of the instrument, I would apply the adjustments to the stage.
The experimental instrument of glasses described in 1863 performs admirably, on a white enamelled watch-case, on the surface of a flea, on solid deal, on mouse’s hair, and on the surface of the pollens of whin, broom, and geranium, without condenser. The field is remarkably flat, and available at every part.—FRED. CURTIS, 44, Church Street, Stoke Newington, N.
The Rev. M. J. Berkeley and Mr. Hogg
—In the January number of the Journal, p. 21, Mr. Jabez Hogg has brought a charge of inconsistency against me which is quite unfounded.
In the first place, the passage in the ‘Outlines’ cited by him does not run “it is possible,” but “it is probable.” And, in the next place, it does not refer to cutaneous affections at all, but to those of the mucous membranes. There is not, therefore, the inconsistency with which he charges me. Moreover, I have not cited Mr. Lowe as an authority for the production of diseases by the rubbing in of the spores of fungi. What I say is, that “Dr. Lowe has induced skin-diseases by inoculation with the granules of yeast, and he is inclined to attribute a great deal more to the agency of fungi than has hitherto been allowed.”—Outlines of Brit. Fungology.