57 



a lb. to the square foot. The fall of rain was not remarkable. The 

 extreme force of the gust was at its beginning, the pressure declining 

 in 15m from 20 to 15 lbs. and reaching 3^ lbs. at Ih 10m, when it 

 again increased. At the regular observation of the barometer, about 

 twenty minutes past 6 o'clock, the wind having then the direction of 

 N. W. by W. and a force of nearly 201bs., the barometer stood at 

 29.548 inches, (corrected,) the temperature of the air being 50°, and 

 the elastic force of vapour calculated from the evaporating point, 

 and temperature being 0.357 inches. The rise of the barometer be- 

 tween the 4 and 6 o'clock observations, had been but .06 of an inch, 

 and the pressure continued to increase during the night. The force 

 of this storm is almost exactly that assigned in the table attached to 

 the report of the Committee of Physics of the Royal Society of Lon- 

 don, to a "great storm." It is to be regretted that an observation 

 was not taken immediately preceding the storm, to know if there was 

 a sudden fall of the barometer at that period. 



Prof. Bache also described to the Society a modification of 

 the part of Ostler's self-registering anemometer, which mea- 

 sures the force, made by Mr. S. W. Hall, first assistant at the 

 Magnetic Observatory at the Girard College, and applied to 

 the instrument there. 



It consists in substituting slightly curved bars or nearly flat springs 

 attached to the table or frame of the registering part of the instru- 

 ment, for the spiral springs applied in the original instrument behind 

 the plate which receives the impulse of the wind. One only of these 

 springs acts in measuring the force of light breezes, and the second 

 is brought into play in stronger winds. The sensibility of the instru- 

 ment is much increased in winds below five pounds to the square 

 inch, while the instrument retains the range of the original one. The 

 friction of the apparatus necessary to guide the spring, and the expo- 

 sure of the spring to the weather and to great fluctuations of tempera- 

 ture are avoided. The springs being in the recording room, their 

 action may be observed at any time, and repairs or changes required 

 may be readily made. The removal of a considerable weight from 

 near the top of the vane and greater compactness are further advan- 

 tages of this modification of the original plan. The springs actually 

 used are of hammered brass. 



Mr. Lea, on behalf of the Publication Committee, reported 

 that all the papers which had been ordered to be published in 

 the Transactions were in type. 



