422 
PROCEEDINGS OF THE SOCIETY. 
authorities at Milan had shown conspicuous judgment in their recogni- 
tion of Marzoli’s skill by the award of a silver medal. He trusted the 
Society would give the lens most careful guardianship in their cabinet of 
apparatus, and that he should be empowered to express officially to 
Messrs. Trainini their high appreciation of the donation. 
The Chairman said the Society were much indebted to their Secretary, 
Mr. Mayall, for his very interesting communication, and he had much 
pleasure in proposing, first, that the best thanks of the Society be given 
to their Secretary for his energy, tact, and perseverance in following up 
the subject, and for bringing it before them in the way he had done ; 
and, secondly, that their best thanks be also given to the donors of the 
lens, and that the Secretary be requested to assure them of the high 
value in which it was held, and always would be held, by them as 
a Society. 
Mr. Charters White inquired if it was known what was used for the 
purpose of cementing the lenses together, Canada balsam being at that 
time unknown ? 
Mr. Mayall thought it was not quite certain that Canada balsam was 
unknown then ; but it was a fact that Clairaut, the eminent French 
mathematician of the last century, had proposed that lenses might be 
cemented together, believing that he had thus suggested an important 
improvement upon Dollond’s uncemented achromatic telescope object- 
glasses. 
Mr. Powell said that gum mastic was frequently used for the purpose ; 
his firm many years ago used it constantly. 
Mr. Mayall said it would be remembered that at the last meeting 
Mr. Goodwin brought forward an eye-piece for which some advantages 
were claimed. Almost immediately after that meeting he received a 
note from Mr. Philip Vallance, who, having seen a report of Mr. Good- 
win’s communication, wrote to say that he had in his possession two eye- 
pieces which were made for him on the same plan nearly forty years ago 
by Mr. Murrell. Mr. Mayall said, as a matter of fact, this form was 
very old indeed, dating from about 1667. Mention was made of one 
like it in the ‘Philosophical Transactions,’ constructed by Eustachio 
Divini shortly after the publication of Hooke’s ‘ Micrographia,’ 1665. 
In Birch’s ‘History of the Koyal Society,’ an extract from the Society’s 
minutes showed that Christopher Cock, the optician who worked for 
Hooke, was requested to exhibit at the Society a large Microscope having 
such an eye-piece. Later on Grindl, of Aix-la-Chapelle, mentioned the 
same thing, and it had been also employed by others, with more or less 
modification, throughout the last century, and later. Then with regard 
to the other point of novelty claimed by Mr. Goodwin — the possibility 
of adjustment — it seemed that in those which Mr. Philip Vallance 
had made for him there was a screw provided which enabled the com- 
pound eye-lens to be adjusted, with reference to the field-lens, through 
a space of nearly 1/2 in. 
Mr. E- M. Nelson read a paper on “Micrometers,” in the course of 
which he described a new micrometer made for him by Messrs. Powell 
and Lealand. The subject was illustrated by a drawing upon the board. 
