HARDWICKE'S SCIENCE- GO SSIP. 



59 



slung upon a long pole in order to protect its occu- 

 pant from injury arising from violent contact with 

 the sides of its prison, brought about by the motion 

 of the vessel. On being placed in the gardens, it 

 soon became quite tame, and fed readily on lettuces 

 and sliced vegetable marrows. This lasted till the 

 7th of September, when the animal died very sud- 

 denly ; an examination of the body by Mr. Garrod, 

 failing to discover the cause of death. 



The remaining species of Manatee, Manatus sene- 

 galensis, has been found in the Senegal, the Gambia, 

 and some of the rivers of Western Africa. Murray 

 (" Geographical Distribution of the Mammals") says 

 that its range extends round the Cape of Good 

 Hope, and that it has been found as far north on 

 the other side of the continent as Quillimane, in 

 Mozambique. The skull of this species, according 

 to Dr. Balfour Blaikie (P.Z.S., 1857, p. 30), differs 

 from that of M. americanus in being more compact, 

 the snout shorter, the lower jaw more angular, with 

 its lower border more curved, and the zygomatic 

 process of the temporal is less elevated. Its habits 

 appear to be similar to those of the preceding 

 species ; frequenting the estuaries of rivers, it feeds 

 on the marine vegetation there abounding; but as a 

 species it is not nearly so well known as its Ame- 

 rican relative. 



(To be continued.) 



PHOTO-MICROGRAPHY. 

 By T. H. Powell. 



THERE is a general impression that it is not 

 easy to obtain a good negative when a photo- 

 graph of a microscopic object is desired; and that 

 the difficulties are in many cases great cannot be 

 denied. There are many objects, however, which 

 may be easily photographed; and the aim of this 

 paper is to give simple and concise directions 

 whereby this may be done. 



A special photographic camera is not necessary, 

 because, in focussing, the body of the microscope is 

 moved, and not the focussing-glass. An ordinary 

 camera, with lens removed, can therefore be used, 

 with a piece of very finely ground glass fitting the 

 frame carried by the dark slide, as a focussing-glass, 

 held tightly in its place by springs so arranged that 

 the glass can be removed readily before the sen- 

 sitized plate is taken out of the bath ; it being most 

 essential that the sensitized plate should lie in 

 exactly the same plane as the focussing-glass. 

 Erames, measuring 4i by 3| in. or 5 by 4 in., will 

 be found most handy, and should be well varnished, 

 and great care taken to keep the wires clean. The 

 microscope, placed on a table in a horizontal 

 position, must be connected with the camera by a 

 black velvet hood fitting round the tube of the 

 microscope, and must oe perfectly light-tight in 



every part. If the microscope be a binocular, the 

 Wenham prism must be removed ; and it is better 

 to substitute for the eye-piece a brass tube, with a 

 dead blacked interior extruding about a quarter of 

 an inch from the end of the instrument, over which 

 stops of various sizes may be fitted (easily made 

 from pill-box lids, by punching round holes in 

 them). A paraffine lamp can be used for illumina- 

 tion, and admits of two arrangements. It can 

 either be placed at the side, and its light condensed 

 on the mirror beneath the stage by a bull's-eye con- 

 denser, and thence reflected through the object up 

 the microscope tube ; or the mirror can be dispensed 

 with altogether, the lamp placed so that the centre 

 of its flame is in a line with the optical axis of the 

 microscope, and a bull's-eye condenser placed 

 between it and the stage at that distance which 

 yields an intense well-diffused light. If a trans- 

 parent object {e.g., the proboscis of a blow-fly) be 

 now placed upon the stage, its reflected image will 

 be seen upon the focussing-glass ; and this must be 

 examined with a pocket-lens, till, by means of the fine 

 adjustment, the sharpest possible image is obtained. 

 An allowance must now be made for the over-cor- 

 rection of the objective by turning the slow adjust- 

 ment, so that the objective is slightly brought away 

 from the object. For an inch object-glass about 

 one-third of a turn is required ; the exact fraction 

 of a turn can only be ascertained by experiment. 

 For a quarter-inch object-glass the correction re- 

 quired is so slight that it is scarcely necessary. 



Everything is now ready for taking the negative ; 

 for this the following solutions will be required. 



A good bromo- iodized negative collodion 

 (Mawson's answers admirably, and can be obtained 

 anywhere). 



Silver Bath.— Nitrate of silver, 1 oz. ; distilled 

 water, 14 oz. ; nitrate of barium, 40 grains ; dilute 

 nitric acid sufficient to render very slightly acid. 

 When all have dissolved, filter ; and, before using 

 the first time, leave a collodion-coated plate in it 

 for half an hour. 



Iron Developer. — Sulphate of iron, £ oz. ; water, 

 8 oz. ; filter when dissolved, aud add glacial acetic 

 acid, i oz. ; spirit of wine, I oz. 



Redeveloper. — No. 1. Pyrogallic acid, 5 grains; 

 citric acid, 12 grains ; distilled water, 1 oz. No. 2. 

 Nitrate of silver, 10 grains ; distilled water, 1 oz. 



Clearing Solution. — Cyanide of potassium, 80 to 

 120 grains ; distilled water, 10 oz. To be labelled 

 "Poison." 



The plate having had its edges roughened by 

 drawing across the edges of another plate, is ren- 

 dered chemically clean by scouring with a mixture 

 of Tripoli powder one part, methylated spirit and 

 liquid ammonia of each two parts, then washed 

 under a tap till all trace of the mixture is removed, 

 drained, dried, and well polished with a silk hand- 

 kerchief ; next held horizontally and the collodion 



