June 12, 1903.] 



SCIENCE. 



943 



PHILOSOPHICAL SOCIETY OF WASHINGTON. 



Xhb 569tli regular meeting was held May 

 9, 1903. The first paper was by Dr. H. Car- 

 ring-ton Bolton, on ' The Genesis of Hygrom- 

 eters and Anemometers.' 



The earliest recorded instruments for meas- 

 uring the moisture in the atmosphere were 

 those of Nicolas de Cusa, about 1450; they 

 were bits of wool and of sponge fastened to 

 one arm of a balance. Leonardo da Vinci 

 invented a more perfect hygrometer, consist- 

 ing of a metallic ring with a graduated scale 

 which bore at its center a movable rod, to the 

 ends of which were fastened small spheres of 

 metal, one covered with wax and one with 

 cotton wool. Leonardo thought the wax re- 

 pelled moisture and the cotton absorbed it. 



Sanctorius in his ' Medicina statica ' 

 (Venice, 1614) mentions three hygroscopic 

 substances, the ' dregs of alum,' thin boards 

 and strings of a lute. 



The Italian physicists of the Accademia de 

 Cimento employed a conical vessel filled with 

 ice for condensing the moisture of the air. 

 The ingenious Eobert Hooke describes in his 

 ' Micrographia ' (1664) a hygrometer, the es- 

 sential feature being the awn of wild oats. 



The weather-mannikin, still common in Ger- 

 many, was invented in 1685 by Wm. Molineux. 

 In the eighteenth century a very great variety 

 of hygroscopic bodies were employed, from 

 wood through guts of animals to marine algae 

 and deliquescent salts, but De Saussure's hair 

 hygTometer was found to excel. 



John Dalton in 1801 proposed noting the 

 dew point, and Leslie's psychrometer was in- 

 vented about the same date. Daniell's con- 

 densing hygrometer dates from 1820. 



The earliest anemometers were those in- 

 vented about 1578 by Egnatio Dante, a 

 Dominican monk. It is similar to that of 

 Wild's tablet-anemometer reinvented in 1860. 

 The speaker described briefly a large number 

 of instruments for measuring the velocity of 

 the wind down to Eobinson's cup anemometer 

 now in use, first brought out in 1850. 



Dr. Bolton called attention to the fact that 

 every one of the fundamental instruments 



now ^lsed in meteorological observations is of 

 Italian parentage: 



1450 Hygrometer, Nicolas de Cusa. 



1578 Anemometer, Egnatio Dante. 



1595 Thermometer, Galileo. 



1639 Eaingauge, Cartelli. 



1643 Barometer, Torvicelli. 



Mr. E. E. Hayden, of the Naval Observa- 

 tory, then described, with aid of lantern ob- 

 servations, the ' Naval Chronometer and Time 

 Service.' The Navy possesses about 800 

 chronometers, and for the rating of these 

 elaborate provision is made at Washington; 

 further facilities are provided at Mare Island 

 Navy Yard, Cal., and at Cavite. The tests 

 used were described, diagrams were exhibited 

 to show the actual behavior of instruments 

 under service conditions, and the details of 

 the daily telegraphic tirae service were ex- 

 plained. 



The last paper of the evening, by Mr. J. 

 F. Hayford, dealt with the unusual features 

 of the plans of a primary triangulation party 

 of the Coast and Geodetic Survey on the 98th 

 meridian triangulation in 1902. The trian- 

 gulation was done at considerably more than 

 double the usual rate for such work in the 

 past, and at half the usual cost per station 

 occupied iinder similar conditions. The work 

 of a single season furnishes an arc of the 

 meridian 6° long, twice as long as the famous 

 Peruvian arc. The accuracy of the work is 

 fully up to the best standards of the past. 

 The observations were made upon heliotropes 

 in the day hours and upon acetylene lights at 

 night. The light keepers were given their 

 orders by heliograph signals. Many of the 

 observations were taken under apparently bad 

 conditions upon very faint images, or images 

 which were very large and fluctuating wildly. 

 The observing towers, 42 feet high upon an 

 average at each station, were erected by a 

 separate building party of seven men, at an 

 average rate of ten per month, the towers be- 

 ing scattered throughout the whole extent of 

 the arc 446 miles long. No screens were 

 found to be necessary to shelter the inner 

 tower from the sim and wind, although such 

 screens have been regularly used in the past. 



