ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



99 



latter has a double tubular body and a knob by which it may be handled. 

 The feet of the tripod are drilled for screwing to the table, and are pro- 

 vided with leather pads. Glass tinters and a ground -glass screen are 

 supplied, and these are fixed to the front of the lantern by means of clips. 



Aitchison Photometer.* — This photometer is for measuring the 

 loss of light by absorption and reflection in binoculars and telescopes. 

 The instrument comprises, a lamp placed between two screens, the lamp 

 being movable along a finely divided scale, and the screens are set at 

 the extremes of a triangle, of which the scale forms the base. The 

 other sides of the triangle converge upon the observation telescope, 

 which consists of a triangular box with tubes projecting from each side. 

 The tubes facing the screens carry object-glasses, while the third is 

 arranged as an eye-piece. Two prisms are so arranged in the telescope 

 that the light from each screen is made to illuminate half the field as 

 seen in the eye-piece ; the illumination of the field 

 therefore varies according to the distance of the lamp 

 from the screens. If a binocular or telescope be placed 

 between one of the screens and the observation tele- 

 scope, the light can be so moved that the two halves 

 of the field are equally illuminated, and the loss of 

 light is calculated by a reading from the scale. 



Beck's Large Bull's-Eye Condensing Lens. — 

 This is shown in fig. 9, on stand, with raising motion 

 and clamp ; the lens being over the centre of stand. 



Beck's Iris Diaphragm. - 

 able to the above apparatus. 



-This (fig. 10) is attach- 



Figs. 9, 10. 



Sauver's Bridge Object Holder. — This consists of a bridge-shaped 

 plate of metal which is placed on the stage of the Microscope (fig. 11). The 



Fig. 11. 



specimen is held by rubber bands so that its flat surface is held against 

 the under-surface of the bridge, the hole therein allowing of its ex- 

 amination. It is made by R. & J. Beck. 



(4) .Photomicrography. 



Portable Photomicrographic Camera. — This instrument (fig. 12), 

 which was exhibited at the October Meeting, 1905, by E. Moffat, is 

 suitable for travellers, and is only a few ounces in weight ; it will pack up 

 with travelling Microscope in case, and when placed horizontally is quite 

 reliable with oil immersion lenses up to 1000 diameters. A is a telescopic 

 tube, made in three lengths of 6 in. and of aluminium for lightness. 



Catalogue, Optical Convention, p. 230, fig. 1. 



H 2 



