^jTuSCDe^^^ PROCEEDINaS OF SOCIETIES. 833 
Mr. Beck then alluded to the different views entertained by miero- 
scopists on the structure of the scale, and expressed his belief that if 
the Fellows would adopt the plan he had described they would agree 
with his conclusions. 
Mr. Browning explained, in answer to an inquiry by the Presi- 
dent, that Dr. Pigott had been kind enough to show him the markings 
he had observed, of which he (Mr. Browning) made a diagram. 
But beyond this he had been entirely ignorant of the contents of 
Dr. Pigott's paper until he had heard it read that evening. He 
thought it right to mention that Dr. Pigott had dispensed with a 
condenser, and illuminated the objects by the common lamp flame. 
Mr. Browning also said that the eye-piece used by Dr. Pigott was a 
very deep one, but he was not acquainted with its construction. He 
(Mr. Browning) remembered that in a discussion in which he took 
part with Sims, Dallmeyer, and Prichard, that they all agreed that the 
diffraction-rings of the stars to which allusion was made by Dr. Pigott 
were due to the undulations of light, but if the object-glass were well 
made no perceptible difference in the diffraction-rings would be 
remarked. In reply to a question from Mr. Slack as to whether it 
was not a fact that in the case of two telescope glasses, the one well 
corrected, the other having a considerable residue of spherical aber- 
ration, that the well-made glass would show the diffraction- rings clear 
and sharp, and in the other they would become intermingled and 
indistinct. Mr. Browning said that it was undoubtedly the case. 
Mr. Hogg said he thought Dr. Pigott in error in what he had 
stated in regard to the marking on the Podura scale. He believed 
that Mr. R. Beck was nearer the truth in his view of the structure of 
the scale, especially as the experience of Mr. Mclntyre confirmed his 
opinion. He (Mr. Hogg) had a great objection to the use of too deep 
an eye-piece, as it tended to increase errors ; and he believed that this 
was one cause of the mistake into which Dr. Pigott had evidently 
fallen. He had also erred, he thought, in the method of illumina- 
tion employed, for by using the direct flame of the lamp without any 
means of correcting the illuminating pencil, he would experience 
considerable disturbing power. He objected also to Dr. Pigott's 
mode of obtaining magnifying power by increasing the length of the 
body of the microscope. Moreover, it was well known that as age 
increased and presbyopia set in, the eye was often the subject of certain 
elements of visual disturbance. He thought some such disturbing 
element had led Dr. Pigott to believe that the appearances which he 
had represented were something entirely new. He (Mr. Hogg) had 
examined the scales with immersion lenses, and failed to discover 
anything at all resembling that which Dr. Pigott had described in 
his paper. 
The President said he quite concurred in the observations made 
by Mr. Hogg, and he was only sorry that Dr. Pigott was not present 
to make a reply. He could not but feel (such was his confidence in 
the skill of the opticians of the day) that what he saw with their 
instruments was that which really existed, and that he had a clear 
and correct view of the objects under examination. With respect to 
Podura scale, he believed that Mr. Beck's description of the outline 
