^4 SUMMARY OF CUKEENT RESEAECHES RELATING TO 



pillar, rectangular in section, is provided with inclination joint and 

 clamping lever to secure the instrument in any position by means of 

 vertical and horizontal stops. The arm is of handle type and of enlarged 

 •design ; it provides ample space for manipulation of object. The body- 

 tube has 39 mm. of outside diameter, and is provided with society screw 

 thread ; the oculars are the Bausch and Lomb standard sized eye-pieces. 

 The draw-tube is graduated in single millimetres, with every tenth line 

 numbered. The coarse-adjustment is by standard rack and pinion, and 

 has a stop to prevent pinion from over-riding rack. The fine-adjustment 

 is of lever type, with milled micrometer screw head in two parts for slow 

 and rapid movement, the larger graduated into 100 divisions, each equal 

 to 0* 002,5 mm. in vertical movement, and provided with hinged 

 indicator, which may be turned back from head ; the fine-adjustment 

 ceases to operate when objective touches specimen. The vertical 

 illuminator is a plane glass reflector, readily adjustable, provided with 

 three different sizes in revolving sleeve. The stage is adjustable 

 vertically by standard rack and pinion to increase working distance and 

 allow focusing without displacing vertical illuminator with reference to 

 light ; it is circular in shape, 102 mm. in diameter, with distance of 

 75 mm. from centre to base of arm ; it is made of metal with vulcanite 

 top, and is provided with centring screws and spring clips, removable 

 for substitution of attachable mechanical stage. The mirror is plane 

 and concave, 50 mm. in diameter, and adjustable in two planes in a fork 



mounting. 



f3) llluminatingr and other Apparatus. 



Interference Refractometer.* — E. S. Williams, in pointing out the 

 importance of measuring the refractive index of liquids in estimating 

 their purity, observes that the effect of temperature can be best elimi- 

 nated by measuring, not the absolute refractive index, but the index 

 relatively to some standard liquid in the same bath. But while a 

 refractometer of the Abbe type, for absolute values, gives results reliable 

 to two units in the fourth decimal place, much greater accuracy can be 

 obtained from an instrument which depends on the interference of light 

 waves. The author finds that with such a refractometer a refractive 

 index may be measured with an accuracy of from 0*00006 to O'OOOOOOS, 

 which is, of course, far beyond the capabilities of a refractometer of the 

 Abbe or Pulfrich type. 



Use of the Stereoscope for Examining Superposed Projections.f— 

 H. Hubert believes that his appHcation of the stereoscope to the exami- 

 nation of suspended orthogonal projections is a novelty, and he seems to 

 find it very successful. As an example he quotes the superposition of a 

 topographical surface and an underlying geologic layer. In the ordinary 

 manner superposition of such surfaces would be very confused, while the 

 superposition of three surfaces would be hopeless. But stereoscopic 



* Journ. Inst. Brewing, xxiii. (1917) pp. 457-60 (3 figs.), 

 t Comptes Rendus, clxv. (1917) pp. 1059-60. 



