840 
PROCEEDINGS OF THE SOCIETY. 
whether this appearance was due to ingested food or to some other 
cause it was impossible to say.” 
A circular letter was read from Dr. A. M. Edwards, of Newark, 
New Jersey, U.S.A. asking for samples of diatomaceous earth from this 
country in exchange (or otherwise) for similar material from Cali- 
fornia. 
Mr. F. Chapman read his paper “ On the Foraminifera of the Gault 
of Folkestone.” (See ante , p. 561.) 
The Secretary, in thanking Mr. Chapman for his paper, said it had 
been very strongly recommended to the Publication Committee by 
Prof. Judd and also by Prof. Eupert Jones. 
Sir Walter Sendall, K.C.M.G., exhibited and described a new appa- 
ratus which he had devised for making more accurate measurements of 
microscopic objects than were possible with the camera lucida, the 
inherent faults of which were explained by drawings on the blackboard. 
Mr. E. M. Nelson said he had listened with much interest to this 
paper, and was very pleased to find that original thought was being 
brought to bear upon this subject by one who said he was a beginner. 
There could be no doubt that camera lucida measurements, when made 
in the ordinary way as described, were grossly incorrect, and that the 
apparatus which had been devised to enable corrections to be made was 
most ingenious and thoroughly scientific in principle. He thought, 
however, that there was a much simpler method of obtaining true 
measurements, by projecting the image for a much longer distance than 
the usual 10 in. ; if, for instance, it was projected to a distance of 
5 ft. the curve would with so large a radius be practically reduced to 
a straight line and measurements could then be made with very great 
accuracy. The camera lucida and neutral tint reflector were rough and 
ready means and useful only for ready reference ; where expense was 
not an object and correctness was of importance the eye-piece micrometer 
would best meet the requirements. It occurred to him that in using the 
ordinary camera lucida another element of error was introduced in con- 
sequence of the refraction which took place when rays passed through 
at an angle. As regarded the remarks made about the ruled lines in 
micrometers, it was quite true that the first methods adopted were open 
to some objection, but the ruling was now done so perfectly that it was 
possible to arrive at measurements even as small as 1/500,000 in. with 
a far greater accuracy than could be attained with any machine. Fasoldt 
and others had ruled lines up to 1/200,000 in. apart, though they had 
only been seen up to 1/100,000. He had been very much interested 
in the description of this contrivance, which he thought would be very 
bandy for rough measurements. 
Mr. Michael said he had contended for many years that this question 
of curvature invalidated not only all camera lucida measurements, but 
all camera drawings as well, and for this reason he had long since 
abandoned the process and had used the eye piece micrometer instead. 
Mr. C. Beck said it might comfort some microscopists present who, 
after what had been said, felt inclined to throw away their camera 
