Oct. 1, 1S6C] 



HAEDWICKE'S SCIENCE-GOSSIP. 



233 



Fig. 224. 



MICROSCOPY. 



A Hand-glass.— The great objection I have 

 found to the Coddington and Stanhope Lens, &c., 

 which applies equally to the Stanhopescope, is, that 

 the focus is fixed, and so does not suit 

 different eyes nicely, and cannot be 

 altered for the thickness of an object. 

 Now this is prevented by a small in- 

 strument I have made for one or 

 another, and which I have found much 

 liked. It consists of a short tube with 

 a little handle. At one end is fixed 

 a plano-convex lens, about -J-inch 

 focus. This tube has another screwed 

 into it, with a similar lens about 

 7' -inch focus. The adjustment is by 

 the screw. These properly made, and 

 the screw home, both lenses may be 

 used as a single power. The figure is about the 

 size. The focus of the lenses may be altered for 

 increased power. — E. T. Scott. 



A " Finder." — A correspondent in your last 

 number expresses surprise that few microscopists 

 use " Maltwood's Finder " for registering the posi- 

 tion of minute objects, or parts of objects upon the 

 slide upon which they are mounted. I must beg to 

 join with him, so far as the need and convenience of 

 a finder is concerned ; although, in my opinion, the 

 end can be attained in a far more simple manner 

 than by the use of a separate piece of apparatus. 

 So far as my own experience goes also, it can be 

 attained with greater accuracy, without extra appa- 

 ratus. Your correspondent points out. that when 

 "ith, Hh, or y^jth powers are used, the figures alone 

 (on Maltwood's Finder) are not sufficient for imme- 

 diate re-discovery of minute objects." Now it is 

 precisely with these powers that a proper system of 

 registration and finding is most useful. It is but 

 seldom that we find each frustule of a diatom pre- 

 cisely like its fellow — there is some difference in 

 position or detail ; and in testing the definition of 

 object-glasses, or ascertaining the value of different 

 kinds of illumination, it is desirable always to use 

 the same diatom, or portion of one, with which the 

 eye is accustomed. Frequently, too, in slides on 

 which several species are mounted, there are some 

 individuals which are uncommon or even unique, 

 and so small as to be only properly shown by a high 

 power. It is very vexatious to have to spend a 

 quarter of an hour in hunting over a slide for the 

 required specimen ; and the method of indicating 

 the neighbourhood of the object by a dot of ink is 

 too uncertain and too clumsy to be trusted. Some 

 years ago the Microscopical Society of London had 

 the question of " finders " under their consideration 

 by a committee, but nothing came of it. At that 

 time I pointed out what I considered to be the 



simplest method of procedure, and since then I 

 have never found it fail. It is simply to engrave 

 on the stage of the microscope a scale of divisors, 

 say 50 to the inch. This can be doue on any instru- 

 ment. If the stage be provided with motions at 

 right angles, the divisions should be so marked as 

 to measure the amount of motion of the object-plate 

 in either direction. A stud should be planted on the 

 object-plate, and if the slide be touching this, all 

 that has to be done when the object has once been 

 found and placed in the centre of the field is to read 

 off the " latitude " or distance from the side, and the 

 "longitude" or distance from the end, and mark 

 the figures with ink on the label. At any future 

 time, if the indef of each stage-slide be made to 

 point to the divisions so registered, the spot will be 

 in the field, or be so close as to be easily found. 

 The same plan can be applied to the plain stage 

 with a sliding-ledge, the edge of which may pass 

 over the scale of divisors, and would register " lati- 

 tude." Another scale should be engraved on the 

 ledge itself, which would indicate " longitude " by 

 the end of the glass slide. A slide registered by 

 one instrument would read off the same on any 

 other, provided, of course, that the same unit of 

 division was used, and the scales were properly 

 planted so as to read from a fixed distance from the 

 axis of the object-glass, so as to measure ^Vth of an 

 inch for, say, half an inch in either direction. An 

 observer might then send a slide to any distance to 

 a friend, and direct his attention infallibly to the 

 particular detail he wished. It is to be regretted 

 that so simple a method of registering is not gene- 

 rally provided by makers of microscopes. It would 

 cost but a shilling or two to engrave the necessary 

 divisions on the stage-plate, and the convenience 

 would be great.— W. Hislop. 



Microscopic Camera-obscura. — In all books 

 on the microscope that have come under my notice, 

 the camera-lucida has been the only form put for- 

 ward as advantageous for drawing the magnified 

 image. I don't know how others find it, but I 

 certainly do not like either the cramped stooping 

 position necessary to its use, nor does it contribute 

 to accuracy of tracing. I have, therefore, for some 

 time past, been in the habit of using the camera- 

 obacara in preference ; and as some of your readers 

 may be unacquainted with its capabilities when 

 applied to the microscope, the following description 

 may be acceptable : — I remove the cover of the eye- 

 piece, and in place of the usual camera-lucida 

 reflecting-glass, I substitute a right-angled prism 

 fitted in a short tube, so that it can be placed close 

 to or removed from the eyepiece for adjustment. I 

 have had constructed a wooden frame, exactly like 

 a box without a lid. Placing this on a table on end, 

 with the open side next the observer, I pass the 

 tube of the microscope through a slit in front (this 



