MAR. 4, 1923 PROCEEDINGS: PHILOSOFHICAL SOCIETY 91 
PROCEEDINGS OF THE ACADEMY AND AFFILIATED 
SOCIETIES 
PHILOSOPHICAL SOCIETY 
874TH MEETING 
The 874th meeting was held in the Cosmos Club Auditorium on Saturday, 
December 16, 1922. It was called to order at 8:20 P.M. by President WHITE 
with 33 persons present. 
The minutes of the 872d meeting were read and approved. 
By invitation, Mr. A. H. Bennerr addressed the Society on The aberrations 
of anastigmatic photographic lenses. The address was illustrated by lantern 
slides, and was discussed by Messrs. Wuirr, Hreyi, WILLIAMSON, LAMBERT, 
Pawtinc, L. H. Apams, and PRIEst. 
Author’s Abstract: In the design of photographic lenses, two requirements 
are dealt with which are not often found combined in other types of optical 
design. 
In the first place, the photographic lens must have a wide angular field 
of view, which commonly ranges from 40° to 60°. In addition, a large relative 
aperture is necessary in order that the lens should have sufficient rapidity. 
These two requirements prohibit an extremely fine correction for the aber- 
rations. 
The definitions, general effects on the defining power of the lens, and 
suitable method of plotting graphs of the aberrrations, together with methods 
of measurement were given. Average values for the magnitudes of the differ- 
ent aberrations as found from a series of measurements on twenty-five (25) 
lenses made by eight manufacturers, were presented. 
Improvement in this type of lens by the employment of aspherical sur- 
faces, which are more favorable for the correction of the aberrations, will 
probably result in a great increase in relative aperture, without increasing 
the aberrations beyond their present values. 
Mr. 8. P. Fergusson and Mr. R. N. Covert presented a paper on The 
measurement of the wind, which was read by Mr. Frrausson. The address 
was illustrated by lantern slides, and various types of anemometers were 
exhibited. The paper was discussed by Messrs. Wuirs, Prisst, L. J. Bricas, 
Heck, and HARPER. 
Author’s Abstract: A review of the progress of anemometry during the 
past century shows very clearly that much of the confusion or discordance 
in data of the direction and velocity of the wind is due to the absence of 
definitions. It is not necessarily difficult to rate an anemometer with a 
precision satisfactory for most uses, but, if there is considerable difference 
in the frequency of readings the indications of two similar instruments may 
disagree as much as 50 per cent and both be correct. The cause of this is 
the extreme variability of the wind, of which the direct fluctuations may 
extend 50 per cent or more on either side of the average velocity prevailing 
during a period of time exceeding one minute; ten or more oscillations may 
occur in one second. The extreme range of mean velocity, or the movement 
of the wind during periods of five minutes or longer (published in current 
reports), extends from a calm to about 60 meters a second, the latter velocity 
occurring sometimes at exposed stations. At most inland stations, however, 
the extreme velocity of gales seldom exceeds 30 meters a second. Another 
characteristic of the wind, of considerable importance in the design of ane- 
