52 



SCIENCE-GOSSIP. 



[Mapch 1, 1SG6. 



lias been — nay, I believe is, alive in our "glass 

 seas"), the pouch is immediately under the tail; in 

 Dori/rha/iipJius, the pouch is on the breast ; in 

 Nerophis, the eggs are placed in rows on the under 

 surface of the body, and not encased in pouches at 

 all. But space bids me close. In my next I shall 

 Lave more to say about these pipe and other " odd 

 Gshes " that play similar eccentric pranks in the 

 management of their families. 



J. K. Loud, F.Z.S. 



THE SPECTRUM MICROSCOPE. 



MR. Ii. C. SORBY has contributed an interest- 

 ing article on this subject to the Popular 

 Science Review, from which we make the following 

 extracts : — 



"Every one is in the constant habit of distinguish- 

 ing different objects by their colour. In many cases 

 this is sufficient to characterize various small bodies 

 seen with the microscope. Now, strictly speaking, 

 spectrum analysis is nothing more than a refined and 

 scientific method of applying the same principle, and 

 the spectrum microscope is simply an instrument 

 which enables us to employ it in the case of very 

 small objects. It is a more refined method, because 

 we may have a number of different substances so 

 nearly of the same colour, that it would not enable us 

 to tell one from another ; and yet, when examined 

 with a spectroscope, their spectra might be entirely 

 different and quite characteristic. On the contrary, 

 we may have cases where the presence of foreign 

 colouring matter so entirely disguises the natural 

 colour of a substance, that its presence would 

 scarcely be expected : and yet, when examined with 

 a spectroscope, the spectrum may be so character- 

 istic, that its presence is perfectly well established. 

 In these remarks I refer to coloured solids or liquids. 

 The spectroscope has been so commonly restricted 

 to the examination of coloured flames— «'.<?. to the 

 study of the light given off from incandescent 

 vapours — that I have fouud many persons who 

 believed, that in order to obtain the spectrum of 

 such substances as blood it is requisite to burn it. 

 There can be no doubt whatever that, on the whole, 

 the facts to be learned from the study of mineral 

 matter in the state of incandescent vapour are far 

 more important and decided, because the spectra 

 are far more characteristic ; but still we may learn 

 a number of valuable facts in studying the light 

 transmitted or reflected from solid or liquid coloured 

 substances." 



After describing the apparatus, he directs atten- 

 tion to the objects which may be examined. " The 

 objects most easily obtained, and which furnish us 

 with the greatest variety of spectra, are coloured 

 crystals, coloured solutions, and coloured glasses. 

 The spectrum microscope enables us to examine the 



spectra of very minute crystals, of very small 

 quantities of material in solution, and of small blow- 

 pipe beads. As previously named, the thickness 

 of the object makes a very great difference in 

 the spectrum. For example, an extremely thin 

 crystal of ferridcyanidc of potassium cuts off all 

 the blue rays, and leaves merely red, orange, yellow, 

 and more or less green ; but on increasing the thick- 

 ness, the green and yellow disappear ; and when very 

 much thicker, little else but bright red light is trans- 

 mitted. In all such cases, the apparent magnitude 

 of the effect of an increase in thickness is far greater 

 when the object is thin than when thick, and past a 

 certain thickness the change is comparatively very 

 slight. If only small crystals can be obtained, it is 

 well to mount a number of different thickness ; but 

 when it is possible to obtain crystals of sufficient 

 size, it is far better to make them into wedge-shaped 

 objects, since then the effect of gradual change in 

 thickness can easily be observed. Different kinds 

 of crystals require different treatment, but, as a 

 general rule, I find that it is best to grind them on 

 moderately soft Water-of-Ayr stone with a small 

 quantity of water, which soon becomes a saturated 

 solution, and then to polish them with a little rouge 

 spread on paper laid over a flat surface ; or else, in 

 some cases, to dissolve off a thin layer by carefully 

 rubbing the crystal on moist blotting-paper until the 

 scratches are removed. Then, whenever it is ad- 

 missible, I mount the crystal on a glass, and also 

 cover it with a piece of thin glass with Canada 

 balsam. Strongly coloured solutions may be ex- 

 amined in test-tubes, or may be kept scaled up in 

 small bottles made out of glass tubes, the light then 

 examined being that which passes through the centre 

 of the tube from side to side. Such tubes may be 

 laid on the ordinary stage, or held on the stage at- 

 tached to the eye-piece. Smaller quantities may be 

 examined in cells cut out of thick glass tubes, one 

 side being fixed on the ordinary glass with Canada 

 balsam, like a microscopic object, and the other 

 covered with thin glass, which readily holds on by 

 capillary attraction, or may be cemented fast with 

 gold size or Canada balsam, if it be desirable to keep 

 it as a permanent object. Such tubes may be made 

 of any length that may be required for very slightly- 

 coloured solutions. Cells made out of spirit ther- 

 mometer tubes, so as to be about one-tenth of an 

 inch in diameter, and half an inch long, ate very 

 suitable for the examination of very small quantities ; 

 but where plenty of material can be obtained, it is 

 far better to use cells cut out of strong tube, having 

 an interior diameter of about three-fourths of an 

 inch, cut wedge-shape, so that the thickness of the 

 solution may be one-fourth of an inch, or more, on 

 one side, and not above one-fortieth on the other ; 

 and then the effect of different thicknesses can 

 easily be ascertained." 

 We can only quote one other paragraph, which 



