38 
PROCEEDINGS OF SOCIETIES. 
might be useful to many persons who were interested in the subject, 
and he had therefore much pleasure in offering them for distribution 
amongst the gentlemen present. The scale (which was enlarged upon 
the board by Mr. Stephenson for the purpose of explanation) was 
printed upon a sheet of paper about 141 in. x 10 in., across which, at 
about 1 inch from one end, a straight line was drawn ; and this line 
was bisected by another straight line, which was extended to the 
opposite end of the paper, and along which a scale of cotangents was 
marked from 175° to 35°. (See p. 3.) 
Mr. Slack suggested that if the paper was mounted upon a smooth 
board, and two knife edges of ivory were substituted for the night-lights 
used by Mr. Stephenson, the scale could be used in daylight, and he 
thought with advantage over the lights. 
Mr. Crisp was quite sure that by the time they met again in 
October, Mr. Stephenson would have invented something much better 
for the purpose than night-lights. 
Mr. Wenham thought this had supplied a want : in principle it in 
no way differed from the ordinary way, but was carried out rather 
in a different manner. He was inclined to doubt whether this plan 
would give perfectly accurate results, but he thought it would be 
correct within a degree. 
The President thought as there was a little difficulty in seeing the 
very small images of the lights, it might be better to convert the 
object-glass into a telescope by placing a lens behind it. 
Mr. Wenham said that in using the ordinary sector for the purpose, 
when a glass was properly stopped the angle could be determined very 
accurately ; but with one not properly stopped there was no such sharp 
demarcation, but the light would vanish away gradually almost up to 
180°. 
The thanks of the meeting were voted to Mr. Stephenson for his 
communication. 
Mr. Charles Stewart said that through the kindness of Mr. Badcock 
he had lately been enabled to make an examination of that curious 
creature known to them as Bucephalus polymorjphus. (Drawings of 
the above, together with his remarks, will be found at p. 1.) 
Mr. Badcock thought there was one little j)oint which Mr. 
Stewart had omitted to mention, and this was a dark spot which he 
had observed midway between the central tip of the creature and the 
ventral orifice. 
Mr. Stewart said he was under the impression that this dark spot 
might be the three little concretions before alluded to. The only 
other thing which had not been mentioned was a problematical thing, 
which he wanted to examine further before pronouncing an opinion 
upon. Immediately in front, and dorsal to the sucker, there was a 
considerable sized depression, having underneath it a space apparently 
identical with the elongated space representing the water-vascular 
system. As the creature was dying, he hardly liked to speak with 
certainty about it, but thought it might be the anterior extremity of 
this curved space. 
Mr. Badcock said that another point of interest was the periodical 
