224 PROCEEDINGS OF SOCIETIES. 
Joseph Birdsale Jones and Dr. J. Birkbeck Nevins were elected 
ordinary members. 
The Rev. W. H. Dallinger, F.R.MLS., gave a practical “ Note on 
the Ultimate Limit of Vision,” as applied to our modern micro- 
scopical lenses. Reasoning on certain data more or less theoretical, 
mathematicians of the first order, notably Helmholtz, had concluded 
that the limit of vision had been reached; that the optician could 
practically aid us no further; that, in short, the limits of possibility 
had been arrived at, since light itself is too coarse to reveal objects 
smaller than those visible to our finest and most powerful lenses. 
The limit marked out was about the one hundred and eighty 
thousandth of an inch. But Mr. Dallinger gave instances of a re- 
markable kind—the result of his personal investigation—directed 
specially to this point, which were proved by a method of measure- 
meut employed specially for the purpose to carry the power of our 
most delicately constructed lenses considerably further than the 
mathematician considered possible ; revealing, indeed, smaller objects 
than those mathematically indicated ; and Mr. Dallinger did not by 
any means believe that he had wholly exhausted the utmost power of 
visibility by these experiments. A discussion followed, which was 
chiefly concerned in eliciting more in detail the method employed in 
these delicate measurements. The meeting concluded with the usual 
conversazione, at which there was a good display of microscopes 
and many interesting objects exhibited. 
