688 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



Fig. 144. 



The graduated cirelo of the upper Nicol is so divided that each 

 division corresponds to the rotation produced by 1 per cent, of grape- 

 sugar in the solution at a temperature of 20° Celsius ; and by means 

 of the vernier, readings are made to • 1 per cent. In the case, there- 

 fore, of raw sugar, the percentage must be taken as three-quarters of 

 tlio number of divisions indicated on the scale, that being the ratio of 

 the rotatory powers of raw and grape sugar. In all respects the 

 instrument is used exactly as any saccharometer of similar construc- 

 tion. '1 he advantages claimed for it are that it is cheap, requires no 



special stand or artificial light, 

 and gives tho percentage of sugar 

 in diabetic urine, &c, directly by 

 the vernier readings. 



Baker's New Microscope 

 Lamp. — This lamp (fig. 144) is a 

 simplified and economical form 

 of the one recommended * by 

 Mr. E. M. Nelson for high-power 

 work. Its chief advantages are 

 that the flame can be used much 

 nearer the table than in the 

 ordinary Microscope lamps, while 

 the dark-chamber metal chimney 

 is arranged to receive a 3 X 1 in. 

 slip, which can be of white, blue, 

 or ground glass. Brass plates 

 with various sized slots for regu- 

 lating the amount of light can 

 also be inserted in front of the 

 glass slip. 



The metal chimney can be 

 adapted to any ordinary paraffin 

 lamp. 



Examination of Graduated 

 Circles with two and four Micro- 

 scopes.! — When the errors of a 

 divided circle are to be determined 

 microscopically for small arcs 

 round the whole circle, a very 

 large number of observations is required. Dr. 0. Schreiber investigates 

 the general theory of the problem, and shows how it may be simplified 

 in practice by a suitable selection and arrangement of the observa- 

 tions. The divided circle is fixed and is centered on a disc which is 

 free to rotate ; the Microscopes can be moved independently of one 

 another about the centre of the disc, so as to traverse the whole circle. 

 Given a certain number of divisions on the circle and a certain 

 number of Microscopes, the theoretically perfect method would make 



* See this Journal, iv. (1884) p. 125. 



t Zeitschr. f. Instrunientenk., vi. (1886) pp. 1-5, 47-55, 93-104. 



