PK0CEEDING3 OF SOCIETIES. 199 



tliat with most microscopists the polariscope was merely a toy to 

 show pretty objects, whereas he believed it ought to be applied more 

 than it was to the making out of structm-e. Having inquired of Mr. 

 Cui'ties respecting Hislop's selenite stage, he was informed that Mr. 

 Ackland had contrived a very simple one, which he thought he could 

 borrow ; but he had done better, for he had induced Mr. Ackland to 

 come down to exhibit and explain his selenite stage. 



Mr, Wonfor considered a large nimiber of microscopists used the 

 polariscope as a scientific instrument in making out structiu-es. 



Mr. Ackland was siu'e the majority used it as a toy, he might say 

 fifteen out of twenty. Scarcely any had a selenite plate with the axis 

 marked. He did not think once in twenty years had he been asked to 

 mark the axis. 



Mr. Wonfor thoiight that a large amount of work was done by 

 microscopists without using the selenite at all, and then only with 

 objects possessing slight depolarizing power. They would all feel 

 obliged by Mr. Ackland's pointing out the advantages of marking the 

 axis. 



Mr. Ackland said, if the axis of the selenite film was marked, 

 it was possible to determine the tension of any object, especially, say, 

 in the examination of muscular fibre, did it point out the direction of 

 the tension. The Germans, who were greatly in advance of us in 

 minute anatomy, always used marked selenites. One of the only 

 persons he knew using one in London, was Mr. Stewart, of St. 

 Bartholomew's Hospital. Selenite films, giving the various tints, blue, 

 green, yellow, red and purple, were commonly used ; but all must 

 have noticed, when examining an object which did not fill the field of 

 view, that the coloiu* of the backgroimd did not harmonize with the 

 colours of the object. It occru-red to him that a neutral tint, cor- 

 responding to the tint occurring in Newton's rings, midway between 

 the violet of the second wave and the indigo of the third wave, was 

 the one required. In a parcel of 500 films he only found one giving 

 this tint ; using it with an object he was delighted with the effect ; 

 happening to put a diiplicate object, which, with an ordinary film, 

 gave exactly the same coloiu's, he was striick with its comparative 

 poorness. Trying the fii'st slide again, he obtained the same good 

 result. This difference, he thought, was either owing to the thin 

 glass cover being at the right axis for the coloui", or the glycerine in 

 which it was moimted exerting an influence. As the neutral films 

 were so difficult to obtain, he had tried a plan of rotating two films, 

 the one over the other, and thus obtained the neutral tint, so delicate 

 in action that its colour varied by the slightest depolarizing influ- 

 ence of the object examined ; and, in addition, gave a display of 

 colours more varied and gorgeous than could be obtained by any of the 

 usual coloui's emj)loyed. At the same time, the rotation of one or 

 other of the films gave a succession of nearly all the prismatic colours, 

 so that, if dissatisfied with the neutral tint, a multiplicity of others 

 could be produced. He had brought with him several selenite stages 

 which could be tested by the gentlemen present. 



Mr. Wonfor, in moving a vote of thanks, said they were not only 



