PROCEEDINGS OF THE SOCIETY. 
905 
It was perhaps not quite correct to say that every portion was of 
aluminium, because there were certain mechanical difficulties met with 
which prevented some portions from being made of that metal ; for 
instance, he believed that it was almost impossible to cut a fine screw 
upon it, without the thread “ stripping,” and it was also found extremely 
difficult to solder, so that the necessary screws in the instrument were 
made of brass, and the Campbell fine-adjustment was of steel ; the rack 
and pinion of the coarse-adjustment were also not made of aluminium to 
avoid the effects of wear, and the nose-piece was of German silver. The 
Microscope was — as they would see — made on Mr. Swift’s well-known 
model. Another difficulty had been to get a good surface finish, since it 
appeared that the ordinary polishing process, such as was employed for 
brass and other metals, was not effective upon aluminium ; he thought, 
however, that the surface was not at all bad, and as aluminium was not 
liable to tarnish from exposure to the air it was unnecessary to lacquer 
articles which were made of it in order to preserve their colour. He 
thought this instrument was well worthy of the attention of the Fellows 
of the Society. 
Prof. F. Jeffrey Bell said that no doubt the Fellows of the Society 
would remember that at their meeting in May last a communication was 
read from Mr. J. C. Wright, of Edinburgh, as to some rotifers which 
he said he had found upon the gills of a newt, but which it was suggested 
at the meeting might have been Vorticellse. Mr. Wright had now 
written to say that he had found that the supposed rotifers were 
Spirochona tintinnabulum. 
Prof. Bell also read a letter which had been received from Mr. H. 
G. A. Wright, of Sydney, with reference to some photographs of Podura 
scales and of the blow-fly’s tongue, in which he says, “In the Feb- 
ruary number of the R.M.S. Journal there is a discussion as to the 
nature of the markings on the Podura scale. A scale on a slide I 
have (purchased about three years ago from Beck) is deeply notched, 
and a little from the bottom of the notch, on the right-hand side, an 
exclamation mark has become detached and projects from the edge ; it is 
plainly shown when observed with an apochromatic 1/12 N.A. 1*4 made 
by Powell and Lealand. Thinking it may be of interest I have photo- 
graphed the upper part of the scale ; unfortunately two or three other 
scales lie behind this portion of the notched scale and render the 
definition less crisp than it otherwise would be. The photograph is 
taken with a Powell and Lealand apochromatic 1/12 N.A. 1*40 (made 
about four years ago) and a No. 3 Zeiss projection eye-piece ; direct 
lamplight is used (edge of flame) and a Powell and Lealand immersion 
condenser N.A. 1*4 (made of the new Jena glass). I also enclose three 
prints of microphotographs of the blow-fly’s tongue, the X 180 shows 
the suckers on the pseudo-tracheae very finely ; this is taken with a dry 
Powell and Lealand apochromatic 1/4 N.A. 1*95 (recently made for 
Dr. Morriss), and the No. 3 Zeiss projection eye-piece, using the edge 
of the lamp flame, and the same condenser as in the photo of the 
Podura scale. The slide of blow-fly’s tongue (photo x 10) was prepared 
1892. 3 p 
