62 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



favorable circumstances of a high dew-point and a calm at- 

 mosphere, both of which conditions were entirely wanting in 

 Chicago at the time of the fire, the air being almost destitute 

 of moisture, and the wind blowing a gale. To produce rain 

 the air must ascend until it becomes cool enough to condense 

 the moisture, which then falls in the form of rain. In the 

 case of Chicago the air could not ascend very far, being driven 

 off in nearly a horizontal direction by the great force of the 

 wind. He presumes, therefore, that this instance neither con- 

 firms nor disproves the Espian theory, and that we may still 

 believe the well-authenticated accounts of instances where 

 rain has been produced by a large fire under favorable cir- 

 cumstances of very moist air and absence of wind. Jour. 

 Frankl. Inst., July, 1872, 46. 



USE OF STEEL WIRE FOR SOUNDINGS. 



An important communication was made by Sir William 

 Thomson to the British Association in regard to the substi- 

 tution of steel wire for the ordinary sounding-lead in deter- 

 mining ocean depths. Usually, if the depths to be measured 

 exceed two or three hundred fathoms, the ordinary sounding- 

 lead becomes insufficient, and a much greater weight must be 

 employed. As a general rule, for each thousand fathoms in 

 depth it is necessary to attach one hundred-weight for the 

 purpose in question ; and consequently, for soundings of two 

 or three thousand fathoms, the weight required becomes enor- 

 mous. The difficulty in raising such a weight has led to the 

 adoption of an arrangement, by which, on touching the bottom, 

 the descending weight is detached and the line drawn up, 

 leaving the weight at the bottom, and, of course, entirely 

 lost. This necessarily involves great expense, and the carry- 

 ing of so many weights adds seriously to the loading of the 

 vessel. 



The size of the cord (usually made of the best Italian hemp) 

 adopted in the British Admiralty is three quarters of an inch 

 in circumference, with a tenacity of half a ton. Steam-power 

 is generally used for bringing back the cord; about thirty-five 

 minutes being required to reach a depth of 2000 fathoms, and 

 forty-five minutes for winding it up. The cord is allowed 

 to run freely off a reel, and the time noted when it ceases to 

 be paid out regularly. The proposition of Sir William 



