544 



SCIENCE. 



[N. S. Vol. XV. No. 379. 



This change in the direction of the compass 

 needle appears to be of a periodic character, 

 requiring' several hundred years for its com- 

 plete develoisment and amounting in the com- 

 pact part of the United States to 5°-8°. The 

 Coast and Geodetic Survey has followed up 

 the phenomenon by observations for the past 

 fifty years, and has now found it possible to 

 deduce certain general relations between the 

 geographic location of a place and the terms 

 of the periodic formula representing the secu- . 

 lar change in declination there. By means 

 of these relations tables have been prepared 

 giving the secular change in declination in 

 each state and territory, and these tables were 

 used in preparing the data for the isogonic 

 chart of the United States for 1&02 which 

 has just been issued by the Coast and Geo- 

 detic Survey. 



In the discussion that followed, Mr. Baker 

 referred to the voluminous magnetic records 

 of the General Land Office, discussed by Mr. 

 Gannett. Mr. Bauer told of the expedition 

 now in the field to locate the magnetic North 

 Pole; and Mr. 0. J. Klotz, of Ottawa, spoke 

 of his own work based on the Canadian obser- 

 vations. 



The next paper was by Mr. C. F. Marvin, 

 of the Weather Bureau, on 'Anemometer 

 Comparisons and the Use of Ball Bearings.' 

 The methods employed in testing anemome- 

 ters on whirling machines were described, and 

 the advantages gained by making the tests in 

 the open air during more or less windy 

 weather pointed out. The artificial wind pro- 

 duced by the whirling-machine motion, com- 

 bined with the natural wind, gives a resultant 

 wind of a constantly changing velocity which 

 resembles closely the gusty winds of nature. 

 From the present state of knowledge of the 

 Eobinson anemometer problem, it appears 

 that each type of anemometer requires to be 

 investigated on its own merits. Anemometers 

 of the same pattern, dimensions, construction 

 and moment of inertia will agree within less 

 than one per cent. In the standard Weather 

 Bureau anemometer the old Robinson law 

 that the cups move one third as fast as the 

 wind is found to be true only for velocities 

 between five and ten miles per hour. The 



cup centers move relatively much faster at 

 higher velocities. Thoroughly satisfactory 

 tests have not been made at high velocities, 

 but the indicated velocities of seventy-five to 

 one hundred miles per hour obtained from 

 time to time in gales and storms are undoubt- 

 edly too high. 



The formula for the standard instruments 

 is found to be 7=0.263 + 2.953i;— .040W; 

 where v is the velocity of the center of 

 the cups and V is the velocity of the wind, by 

 observation up to about 35 miles per hour. 



Speaking of the friction of anemometers it 

 was stated that the popular impression that 

 friction exerted an important influence on the 

 indications of the anemometer was a mistake, 

 and that it was easy to construct instruments 

 even without ball bearings and keep them in 

 such a condition that the friction was an un- 

 important factor in ordinary meteorological 

 work. Friction is of importance only in the 

 measurement of the most feeble air currents. 

 These conclusions resulted from tests made 

 with the whirling machine, and have recently 

 been entirely confirmed by a six-month com- 

 parison of two standard Weather Bureau 

 anemometers, exactly alike in all respects ex- 

 cept that one instrument was fitted with ball 

 bearings of approved construction, while the 

 other instrument was an old one with the 

 ordinary rubbing bearings. In a total run of 

 31,600 miles the ball-bearing anemometer 

 gained 46 miles, viz., 0.15 per cent., on the 

 anemometer with ordinary bearings. This 

 slight difference was doubtless due quite as 

 much to accidental causes as to the large 

 difference in friction which was perfectly 

 apparent to the ordinary perception. 



Charles K. Wead, 



Secretary. 



ANTHROPOLOGICAL SOCIETY OF WASHINGTON. 



The 327th meeting was held February 24. 

 The Secretary to the Board of Managers an- 

 nounced the election to active membership of 

 Dr. O. F. Cook and Lieut. W. E. Safford, 

 U. S. N. 



A Chilkat blanket loom with blanket in 

 process of manufacture was exhibited by Dr. 



