1895. ] NEW YORK ACADEMY OF SCIENCES. 17 
in front of the diaphragm of a manometric capsule and then pho. 
tographing the flames (see Physical Review, Vol. II., No. 10, 
Jan._Feb. 1895). Then counting the waves in each line gives 
the ratio between the vibrations of the two forks. 
The second paper was by J. K. Rees on “ The Penumbrae of 
sun-spots as shown in Rutherfurd’s photographs, with special ref- 
erence to the discussion at the December meeting of the Royal 
_Astronomical Society.” Professor Rees called the attention 
of the Section to the remarks made by the Rey. F. Howlett 
on presenting to the Royal Astronomical Society of London, 
three volumes of sun-spot drawings. This set of volumes con- 
tains drawings made during a period of thirty-five years, and 
shows minute details in regard to the forms and changes of 
solar spots. The Rev. Mr. Howlett stated that his main object 
in continuing the series had been to test the theory put forth by 
Professor Wilson, of Glasgow, in the latter part of the last cen- 
tury. Wilson’s theory claimed that the penumbra in a spot 
shelves down toward the umbra; and that the portion of the 
penumbra nearest the sun’s centre will, therefore, grow narrower 
and narrower, due to perspective, as the sun-spot reaches a 
a point nearer and nearer to the limb. Mr. Howlett claimed 
that his drawings showed that the Wilsonian theory was not 
borne out by his observations as recorded in his drawings. He 
made bold to say that instead of the penumbra of the spot pos- 
sessing shelving sides sloping down toward the umbra, the 
penumbra shows a convex surface ina curve comformable to the 
general contour of the solar surface. He remarked that he had 
not himself witnessed a single case of certain notching of the 
limb. Professor Rees exhibited on the screen a series of fine 
photographs of the solar surface taken by Mr. Rutherfurd with 
his photographie telescope (13 inches diameter of object glass, 
11 feet of focal length) during the year 1870-71. Attention 
was called to the appearance of the penumbral regions of the 
spots, which showed conclusively that the penumbra was as a 
rule eccentric with respect to the umbra. Spots were pointed 
out near the centre of the sun where the penumbral marking 
was deficient, on sometimes the west side, then on the east side, 
