Mabch 26, 1909] 



SCIENCE 



519 



THE PHILOSOPHICAL SOCIETT OF WASHINGTON 



The 661st meeting was held on February 27, 

 1909, Vice-president Abbot in the chair. The fol- 

 lowing papers were read: 

 The Relation letwe&n Sky Polarisation and the 



General Atmospheric Absorption: Mr. H. H. 



TTTMTtAT.T. 



Eayleigh has shown that sky polarization may 

 be attributed to the presence of particles in the 

 atmosphere whose diameters are small as com- 

 pared with the wave-length of light, and the 

 researches of Barus indicate that such particles 

 must be " an integrant part of the air " and 

 " could scarcely be separated from it except by 

 filtration." We can not, therefore, expect marked 

 fluctuations in the intensity of the polarized com- 

 ponent of sky light. 



On the other hand, the intensity of the unpolar- 

 ized component will vary with the amount of light 

 scattered by particles in the atmosphere whose 

 diameters are large as compared with the wave- 

 length of light, and with the amount reflected 

 from the surface of the earth and from clouds. 



Eliminating reflection from clouds, and allow- 

 ing for variations in the reflection from the 

 earth's surface, there remains as a variable factor 

 the scattering of light by large particles in the 

 atmosphere. 



The intensity of the unpolarized component of 

 sky light should, therefore, be a function of the 

 number of such particles present, and conse- 

 quently of the general absorption or diflfusion of 

 light by the atmosphere. 



From observations with an Angstrom pyrhelio- 

 meter and a Pickering polarimeter at the Central 

 Office of the Weather Bureau, an empirical equa- 

 tion has been developed showing the relation be- 

 tween sky polarization and the general atmos- 

 pheric absorption. By means of this equation 

 polarimeter observations are now employed to 

 check the computations of the value of the solar 

 constant from readings of the pyrheliometer and 

 the psyehrometer by a method shown in Bulletin 

 of the Mt. Weather Observatory, Ft. 4, Vol. 1. 

 The results indicate a close relation between sky 

 polarization and the general atmospheric absorp- 

 tion. 



The Principles of Machines for Liquefying &asea: 

 Dr. Edgab Buckingham. 



The speaker discussed the principles involved 

 in the action of simple liquefying machines as 

 distinguished from cascade processes with one or 

 more precooling stages. The total cold available 

 depends only on the pressures between which 



expansion takes place and the initial temperature 

 of the gas; and with the ordinary type of liquefier 

 is quite independent of the internal arrangement 

 of the apparatus. The fraction of the gas that 

 can be liquefied may be computed from its thermal 

 and mechanical properties, if these are known; 

 and the computed values agree very closely with 

 those found by experiment. The increase in yield 

 attainable by avoiding part of the dissipation 

 within the liquefier may also be computed, and 

 is very considerable. Methods for obtaining this 

 improved yield were discussed briefly. 



R. L. Fabis, 

 Secretary 



the academy of science of ST. LOUIS 



The regular meeting was held on Monday, Feb- 

 ruary 1, 1909, at the academy building, 3817 

 Olive Street, the program of the evening having 

 been especially arranged in celebration of the 

 centenary of the birth (February 2, 1809) of Dr. 

 George Engelmann, one of the founders of the 

 academy, and its first president. Standing not 

 only among the leading medical practitioners of 

 the last generation. Dr. Engelmann was also one 

 of the foremost botanists of his day; for, during 

 the many years of an active, useful life, most of 

 which was spent in St. Louis, he found sufficient 

 time, in the leisure hours of his practise, to de- 

 vote to a series of most valuable scientific in- 

 vestigations. And, moreover, in addition to his 

 professional and botanical labors, he was a zeal- 

 ous meteorological observer, keeping observation8 

 pertaining to atmospheric phenomena for over 

 forty years. 



Dr. Bamngarten opened the program of the 

 evening with a very interesting paper, entitled 

 "The Personality of Engelmann." And Dr. 

 Baumgarten, having been a personal friend of the 

 physician and botanist, was peculiarly well fitted 

 to handle this subject, which he treated in a 

 reminiscent way, making characterizations of a 

 personal rather than mere biographical nature. 

 This tribute of Dr. Baumgarten to the memory 

 of his friend was one that bespoke only the most 

 sincere friendship for Dr. Engelmann, and the 

 highest appreciation of his character and 

 achievements. 



Professor H. A. Wheeler presented a paper on 

 " Engelmann's Contributions to Gleognosy." For 

 Engelmann's reputation extended beyond the 

 borders of his master work in botany and his de- 

 votion to local meteorology; although his in- 

 fluence in geognosy is perhaps due less to actual 

 work done in that field than to the stimulation 



