100 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



creasing angular distance from the sun. The method pur- 

 sued was to so adjust the apparatus that an image of the sun 

 would fall upon the Bunsen disk of the photometer, and then 

 to measure the intensity of the light at regular intervals of 

 time, as the sun receded from the portion of the sky whence 

 the light was received. Observations were made on days 

 both hazy and clear; and notwithstanding the 'great differ- 

 ences in the intensity of the light, it was found that it was 

 proportional to some power of the sun's angular distance. 

 This power was approximately for hazy days = 1.04, but for 

 the clearest days =1.21. Proceedings Am. Acad. Arts and 

 ScieticeSj 181 5 f 425. 



WIND VELOCITY AND THE BAROMETRIC GRADIENT. 



The term barometric gradient was introduced into meteor- 

 ology some years ago by an English engineer to express the 

 rate at which the barometric pressure varies as we pass from 

 one part of the country to another. It has long been adopted 

 by Europeans as a rule in weather forecasts, that rapid 

 changes of the pressure or steep barometric gradients will 

 be followed by strong winds blowing nearly at right angles 

 to the direction of the gradient. Tlie explanation of this 

 well-established generalization was partially given some 

 years ago by Professor Ferrel of the United States Coast 

 Survey; and his views have been adopted of late years by 

 most European meteorologists who have studied dynamic 

 laws. According to Professor Ferrel, whenever, from any 

 cause whatever, an influx of air takes place from the sur- 

 rounding regions toward a central spot, a gyratory motion 

 must at once be set up, as illustrated in the whirls at the 

 corners of the streets and in the tornadoes and hurricanes of 

 the tropics. A very slight disturbance in the equilibrium of 

 the atmosphere, such as would scarcely be shown by any but 

 an unusually exact barometer, suflices to initiate the inflow 

 of air and to give rise to the gyrations. If the earth were 

 not revolving upon its axis these gyrations would take place 

 in either direction, viz., either with or contrary to the move- 

 ments of the hands of a watch; but owing to the great power 

 of the immense velocity with which the earth revolves on its 

 axis daily, the direction of all gyratory movements in the 

 northern hemisphere is regulated thereby, being in fact uni- 



