Ape.il 1, IS66.] 



SCIENCE-GOSSIP. 



91 



MICROSCOPY. 



Podura Scale. — The scale figured in last month's 

 Science Gossip is not from Podura plumbea but 

 from a species of Podura which I have only occasion- 

 ally met with. It is much more easily resolved than 

 the scale which is esteemed as a test, and displays 

 its beauty to great advantage under Powell and 

 Lealand's T V obj. Different appearances are pre- 

 sented according to the manner in which it is 

 illuminated ; thus, with the central rays only of the 

 achromatic condenser, the markings which I have 

 figured are shown, while with the peripheral rays 

 (one of the stops being interposed as for diatom 

 illumination), the wedge-shaped particles of the 

 outer lamina; are clearly seen, and each seems to be 

 slightly striated. The " Micrographic Dictionary" 

 says : — " The scales of P. plumbea, the so-called 

 common spring-tail, are usually recommended ; but 

 we believe that the most common Podura is not 

 this species. This is, however, a matter of little 

 importance, because the scales of several species 

 belonging to even different genera, are exactly 

 similar both in form and markings." It appears 

 that the procuring of test scales is somewhat diffi- 

 cult. A celebrated optician showed me the other 

 evening several bottles containing, I should say at a 

 guess, millions of scales, and told me he has spent 

 whole evenings endeavouring to obtain from them a 

 single scale or two exactly equal to his wishes. I 

 have some of the reputed test scales, but prefer the 

 others for display. The last time I found the 

 Podura which is figured, several specimens were 

 caught, and a few more slides made than I want. 

 I shall therefore be glad to exchange with any one 

 for other well-mounted objects of value. — S. J. 

 JSPIntire, Bessborough Gardens. 



Magnifying without either Lens ok Re- 

 flector. — After all is said that can be, in expla- 

 nation of the effects of lenses, whether single or 

 combined in the compound microscope or the tele- 

 scope, our wonder at their marvellous effects is but 

 little diminished. We have come to know much 

 as to how these wondrous effects are brought about, 

 and we have thus ceased, perhaps, to regard them 

 as more mysterious than ordinary natural pheno- 

 mena. But in this knowledge acquired we find 

 fresh matter for astonishment and admiration, in 

 the exceeding simplicity of the means by which 

 results so varied and complex are accomplished. We 

 are now, however, going to say nothing about the 

 optical phenomena produced by lenses, or those by 

 mirrors, and so need not concern ourselves as to 

 how they act. Without calling in the aid of these 

 contrivances, we are going to show how to produce 

 two of the phenomena which are commonly con- 

 sidered to be the peculiar property of these optical 

 contrivances — to show how to magnify minute 

 objects, and how to get inverted images of them. 



Nay, more than this, our apparatus works with 

 complete independence of the laws of refraction and 

 ■reflexion. 



Take a thin, opaque card (black or dark-coloured, 

 by'preference), and make a hole in it with a fine 

 needle, and the apparatus is ready. Do not despise 

 it for its simplicity. A lens is only a piece of 

 glass ; a reflector is only a polished piece of metal ; 

 yet in these lie all the vast powers of the microscope 

 and telescope. Our perforated plate of card or metal 

 plate can, like these, be suitably mounted with ad- 

 vantage. But let us not mind this mounting now. 

 Proceed we to use our easily-acquired instrument. 



Stand facing a bright window or lamp, in a 

 room where there is but one. Hold the card about 

 two inches from the eye so that the light of the 

 window or lamp enters the eye through the hole 

 in it. The hole will then appear as a small circular 

 illuminated field. Now take some small object — 

 the end of a hair or the point of a needle will do 

 — and bring it into this field by holding it between 

 the hole in the card and the eye, say an inch or inch 

 and a half from the latter. There will then be 

 seen, apparently beyond the plane of the card, a 

 magnified image of the object, with a position in 

 the field and a motion across it the reverse of that 

 of the object. 



If the perforated card or thin metallic plate be 

 fastened over one end of an eye-tube, about two 

 inches long, the effect will be more satisfactory, 

 because side-light will be prevented from entering 

 the eye. And if this tube is made of two parts, so 

 as to slide one on the other, it will enable the per- 

 forated plate to be placed at the best distance from 

 the eye. Whatever tube is used must of course 

 have a lateral hole for the introduction of objects. 

 The objects may be supported by forceps, or 

 fastened to a glass slide. If a slide is used with 

 a dark tube there must be two slits made in the 

 latter to allow of the introduction of the slide. 



This interesting fact was communicated to us by 

 the Bev. E. Caswell, of Birmingham. There is no 

 likelihood, we believe, of its receiving any practical 

 application beyond that of a useful illustration of 

 the laws of light. E. D. 



Cleaning Thin Glass. — The usual method is as 

 follows : — Two discs of wood, about two inches in 

 diameter, are procured, one side of each being per- 

 fectly flat and covered with clean wash-leather. To 

 the other side of these a small knob is firmly 

 affixed as a handle, or, where practicable, the whole 

 may be made out of a solid piece. In cleaning thin 

 glass, it should be placed betwixt the covered sides 

 of the discs, and may then be safely rubbed with 

 a sufficient pressure, and so cleaned on both sides 

 by the leather. If greasy, it must be first washed 

 with a strong solution of potash, infusion of nut- 

 galls, or any of the common removing liquids. — 

 Duties on Mounting. 



