438 SCIENCE. 
from Carboniferous, and we have yet to ob- 
tain a much fuller knowledge than we now 
possess of the Devonian fossils of Keewatin 
and the area to the southwest of James Bay. 
J. F. WHITEAVES. 
OTTawa, June 28, 1899. 
SECTION B—PHYSICS. 
Tue work of this section at the Columbus 
meeting was extremely gratifying to those 
who were fortunate enough to attend; al- 
though no papers of an epoch making na- 
ture were presented, still all those which 
were read were of a good character, and 
seemed to represent a large part of the 
work in physics in this country, for the 
past year or more. Several of the papers 
were of considerable importance, and it is 
hoped that they will find their way into the 
columns of this JourNatL before long. 
The meetings of the section were well 
attended and the discussions were intelli- 
gent, interesting and to the point. It 
should be a matter of congratulation that 
the Association succeeded in collecting at 
Columbus so large a number of working 
physicists and presented such a good series 
of papers. It seems that more and more 
such scientists and such papers as are found 
at the meetings of the British Association 
are coming to these meetings. 
The address of the Vice-President, Dr. 
Elihu Thomson, ‘On the Field of Exper- 
imental Research,’ was published in Scr- 
ENCE for August 25th. 
Professor Caldwell presented a number 
of interesting diagrams, which by appro- 
priate super-position enable one to point 
out the constants of current and electromo- 
tive force in the rotary converter. These 
diagrams must be extremely useful in pre- 
senting the complex question of the opera- 
tion of these machines. 
Professor Eddy showed a simple and con- 
venient method for constructing the en- 
tropy-temperature diagrams of a gas or oil 
[N.S. Von. X. No. 248. 
engine from the indicator card ; and showed 
how these diagrams enable one to readily 
detect the advantages or defects in the run- 
ning of such engines. 
Mr. Briggs’ new variable condenser con- 
sists of a series of alternating plates of 
mica and spring brass. The capacity is in- 
creased by compressing the plates together 
by means of a thumb-screw: 
In photometric operations we are accus- 
tomed to compare the relative illumination 
of two surfaces by looking at them, and 
guessing at their relative intensity, or by 
endeavoring to make the illumination of 
the two surfaces equal. In Professor Cat- 
tel’s method, however, the difference be- 
tween the two surfaces is measured by the 
time it requires for the observer to decide 
which of the two surfaces is the brighter; 
it being a fair assumption that the differ- 
ence in the impressions is a function of the 
time required to distinguish between them. 
A considerable series of observations have 
confirmed the belief that this method is not 
only applicable but highly advantageous. 
In Professor Cattell’s other paper, he 
brought before the section an extremely in- 
teresting and novel observation, which must 
throw considerable light upon the relative 
importance of the retina and the brain in - 
the operation of vision. He finds that if, 
by a motion of the eye, the images of black 
and white bars are made to pass over the 
retina at the rate of even a hundred or a 
thousand per second, still the eye or the 
brain perceives them as individual bars, 
and not as a fused gray surface ; of course, 
when the eye is stationary, if light and 
dark images are caused to pass over the 
retina at a much less rate, we have perfect 
fusion. Thus it seems a matter of vital 
importance in distinct vision, when the im- 
age moves.on the retina, whether the eye is 
moving and the object stationary, or the re- 
verse. These experiments indicate that the 
phenomena of vision are chiefly cerebral 
ae 1 - 
