570 PROCEEDINGS OF THE SOCIETY. 



proposed fco Lave the walking-stick sufficiently long to enable the observer 

 to work standing. Quite possibly the conditions would prevent work. 

 but it was hoped sometimes to rig up a net to keep out insects and allow 

 a little work to be done. Mr. Beck did not state what the weight of 

 the Microscope was. Complete in its case, as fitted for use on the table, 

 it weighed two pounds. But even that was far too much to take on 

 such a journey, for, as he had said, only so much could be taken, and 

 the heavier the instruments, the less the quantity of food which could 

 be carried. Therefore, when the difficult journey began, the case of the 

 Microscope would be left behind, the two supplementary legs would be 

 unscrewed, and the Microscope folded up and wrapped in a spare shirt. 

 The weight, without the case, was only one pound. 



Mr. Scales exhibited a variable eye-piece, designed by Mr. M. J. 

 Allan, of Geelong, and a slide of diatoms from the same gentleman. 



Mr. Beck remarked that, unfortunately, he had not had a very long 

 time in which to examine the eye-piece, as he had been very busy. 

 He had made a casual examination of it. It was, as one would 

 expect, a compromise. It was not a first-class eye-piece in any of its 

 conditions. For instance, its best condition was when both lenses 

 were screwed on and it was closed up. It then had a magnifying 

 power of 12| ; it had a slight distortion and fairly good definition at the 

 edge, and moderately good central definition. When one lens was 

 removed and it was drawn out to its fullest extent it was still a 

 moderately good eye-piece, though there was a slight colouring on the 

 fringes at the edge of the field. In that condition it had a magnifying 

 power of about 7^. But in the other cases in which it was used, either 

 with both lenses on and the tube extended, or with one lens on and the 

 tube closed, the marginal definition was extremely bad. There was a 

 considerable colour, and a good deal of pin-cushion distortion. There- 

 fore it was, as one would expect, a compromise between two different 

 powers, between 1\ and 12, with the corrections a good deal marred 

 from the fact that it was a combination. One could not expect the same 

 lenses at different distances to give the same corrections. At any rate 

 that method, although it might be convenient under certain occasional 

 circumstances, did not, he thought, recommend itself, because eye-pieces 

 were very cheap, and he considered that it would be very much more 

 satisfactory to use a couple of really well corrected eye-pieces than one 

 which had not the finest possible corrections in any condition, and was 

 thoroughly bad in some. 



Mr. Scales remarked, with regard to the eye-piece which was sub- 

 mitted to him, that while he agreed with what Mr. Beck said as to it 

 being a compromise, and that it was not, and could not by its construc- 

 tion be properly corrected, he was rather surprised, knowing the imperfect 

 construction of the eye-piece, to find that its definition was as good as it 

 turned out to be. He was also surprised to find that there was not 

 more colour, and that the definition, except at the margin of the field, 

 was fairly good. The maker seemed to have committed the error of 

 trying to get a large field, so that marginal imperfections were not cut 

 off. If he had been content with a smaller field, there would have been 

 a more successful instrument ; but, considering that he had endeavoured 

 to get three eye-pieces into one, he would have anticipated a worse result. 



