HA RD WICKE ' S SCIENCE- G OSSIP. 



9i 



from the front lens of the objective to the eye-lens 

 of the ocular, or from the micrometer on the stage ? 

 And if not to the eye lens, then to where ? If from 

 the micrometer (or other object) on the stage, does 

 that mean that the difference in distance when a 

 2 in. o.g. is in use as against a J in. must be allowed 

 for in the distance from the eye-lens to the drawing- 

 paper ? Second, when deep eye-pieces — No. 4 to 

 No. 6 — are used how am I to proceed ? — there being 

 no cap sliding off to allow the camera (mine is a 

 Beale's) to be put on in its place, but the eye-lens 

 being a fixture in the disc which screws on to the 

 tube containing the field lens, and thus forms a 

 necessary part of the ocular ? I hope I am explicit 

 without being diffuse, and that the information asked 

 for will be kindly furnished in Science-Gossip. — 

 F . R. Brokenskire, Exeter. 



Extract of Logwood . — Perhaps M. Hafen 

 would like to follow the formula recommended by 

 H. Gibbes which is as follows : — Extract of hsema- 

 toxylin, 6 grms., alum (potash), 18 grms. Mix 

 thoroughly in a mortar, add gradually, while stirring : 

 Distilled water, 28 c.c. Filter, and to filtrate add — 

 alcohol (not methylated), 1 drachm. Keep the solu- 

 tion in a stopped bottle for a few days before using. 

 For staining, five to ten drops are to be added to half 

 a watch glass of distilled water ; this solution should 

 be filtered before use. Sections which have been 

 removed from common alcohol, are to be placed in 

 the dilute solution for from ten to twenty minutes, 

 and then to be washed in distilled water. — A. W. L. 



Magnifying Powers. — I am using Howe's 

 " Atlas of Biology." The microscope used in 

 preparing the drawings is one by Zeiss, of Jena. 

 In some instances the magnifying power is indicated 

 thus X 20 ; but in the majority the eye-piece and 

 object glas sused are stated, e.g. D. 3, F. 4. I shall 

 be glad if any reader of Science-Gossip using such 

 a microscope will kindly favour me with a table 

 of the linear magnifying powers obtained by the 

 various combinations of eye - pieces and objectives. 

 — F. Worgau. 



Casting in Plaster from Photographic 

 Cliches. — Mr. Thomas Stock has made the follow- 

 ing communication to the Edinburgh Geological 

 Society : — It is sometimes desirable to convert a 

 photograph (say of certain of the microzoa) into a 

 plaque, which can be mounted on a tablet and 

 exhibited in a case. This can be done by taking 

 plaster casts from reliefs in gelatine. They are 

 productive in two ways. I. On the commercial 

 dry plate ; 2. On cliches of bichromated gelatine. 

 1. On the commercial dry plate. I have experimented 

 with a few makes, but find the gelatine too soft in 

 most cases. One make (possibly containing bichro- 

 mate) gives tolerably good results, but different 

 batches differ in their power of resisting the rather 



severe treatment to which they are subjected. The 

 treatment is quite simple, and consists of dipping the 

 plate (it must not be alumed) for a few moments into 

 water kept at a uniform heat of 90 Fahr. by an 

 automatic gas regulator. I should think that a 

 plate could be put on the market suited to this 

 particular purpose, and its utility in the photo- 

 mechanical printing processes would ensure a steady 

 demand for it. Whilst the relief is still moist and 

 at its best, pour on No. 1 plaster as in ordinary 

 plaster casting, mixed with a little alum to harden 

 it. When dry, the plaster leaves the gelatine without 

 much trouble, no lubricator being needed. The 

 resulting cast may of course be coloured if desired. 

 2. On bichromated gelatine. This method is well- 

 known. It has the great advantage of being capable 

 of giving a higher relief if required according to the 

 thickness of the gelatine. On a moderately hard 

 gelatine, hot water may be used, a fact known almost 

 as long as photography. A little caution must be 

 exercised in the choice of a subject. Their micro- 

 scoped sections are for obvious reasons unsuitable 

 where strict accuracy is required ; but when the 

 lights and darks of the cliches (upon which intaglio 

 and relief depend) nearly correspond to the real 

 intaglio and relief of the object photographed, the 

 resulting cast will of course be accurate as well as 

 beautiful. 



Mr. Fred Enock's Entomological Slides. — 

 No. 9 of these interesting and instructive series has 

 been issued. The slide contains an exquisitely- 

 mounted oak-apple fly {Andricus terminate), and 

 it is accompanied by the usual sketch of structural 

 and other details which gives to these slides their 

 value. 



Coles's "Studies in Microscopical Science." 

 — Sections 1, 2, 3, and 4, of No. 7 issue of these 

 entertaining and artistically got up "Studies" are to 

 hand, dealing with "Vegetable Histology" (Hau- 

 storia), " The Ovary and Ova in Birds," "Patholo- 

 gical Histology " (fatty degeneration of kidney), and 

 "Microbes " (with very useful plate). The illustrations 

 are well up to their high mark ; and the slide accom- 

 panying each " study " is in Mr. Coles's character- 

 istically neatly-mounted manner. 



ZOOLOGY. 



Explosion of Eggs. — In the last number there 

 is an article on "Explosion of Eggs," page 57. I 

 venture to send my late husband's plan for preserving 

 them, which I adopted successfully years before he 

 brought out Science-Gossip :— Dip a soft brush 

 in oil, cover the eggs with it, put them in a jar 

 or pan, be careful to oil over that part of the shell 

 you have touched with your thumb and finger whilst 

 holding it ; put plenty of bran between each layer of 



