PROCEEDINGS OF THE ACADEMY AND AFFILIATED 



SOCIETIES 



THE PHILOSOPHICAL SOCIETY OF AVASHINGTON 



The 718th meeting was held on January 18, 1913, at the Cosmos 

 Club, President Abbot in the chair; about 35 persons present. The 

 minutes of the 716th meeting were read and approved. 



Mr. M. D. Hersey presented a paper on A mechanical model of the 

 least square adjustment. The apparatus exhibited consisted of a sheet 

 of coordinate paper mounted on a board for the plotting of points, a 

 light aluminum rod, and a supply of rubber elastics and push pins. The 

 values under discussion were plotted by the push pins, allowance being 

 made for the unstretched lengths of the elastics by which the bar was 

 suspended. The model was used to show the mechanical adjustment 

 of the tests of a mercury barometer ; the results were compared with those 

 by the usual solution of normal equations. The speaker discussed 

 methods for weighting different observations, the determination of the 

 probable error by the model, and the application of the principle for 

 solution of case involving several unknowns. The paper was discussed 

 by Messrs. White, Rines, and Abbot. 



Mr. H. C. Dickinson presented a paper by himself and Mr. E. F. 

 Mueller on New calorimetric resistance thermometers, describing and 

 exhibiting the improved type of sensitive resistance thermometer devel- 

 oped at the Bureau of Standards. A coil of 0.1 mm. platinum wire is 

 wound on a thin mica strip and enclosed with mica insulation in a plati- 

 num (or silver) sheath pressing firmly on the fiat coil. The upper end 

 of the sheath is fused or soldered to a glass tube carrying the leads. 

 The instrument may be used from — 180° to 500°. The constancy of 

 this type is shown by the fact that for the best of them the resistance 

 at 0° has not changed more than 3 or 4 parts per million in three years, 

 an amount that may be due to impurities in ice used, errors in resist- 

 ance standards, or changes in the leads. Thermometers of this type are 

 now^ being manufactured commercially. Mr. Marvin discussed certain 

 details of their construction. 



Mr. H. L. Curtis spoke on Some properties of electric condensers. 

 A perfect condenser should maintain a constant capacity independent 

 of outside conditions, should have an infinite insulation resistance and 

 no absorption. The problems of construction are mechanical and elec- 

 trical ; the first being to keep the plates so they will have the same area 

 and be the same distance apart, and the second being the insulation 

 resistance and the anomalies of the dielectric. The speaker discussed 

 these problems for the air or gas, mica, paper, and glass condensers. 



296 



