108 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



hope that ohservations of cirrus clouds will in the future be 

 more thoroughly made in connection with weather predic- 

 tions, has been already, we believe, anticipated, so far as the 

 action of the Weather Bureau of the Army Signal-office is 

 concerned, since its tri-daily maps have shown the move- 

 ments of cirri ever since 1871, in which year also Professor 

 Abbe announced for America laws precisely the same as 

 those that Hildebrandsson has now deduced for Europe. 

 Essai sur les Courants Superieurs^ 1875. 



A VERY DELICATE BAEOMETER. 



An ingenious device has been constructed by Mendelef, 

 which shows the slightest variations of pressure by means 

 of a small U-shaped tube containing petroleum- oil. One 

 end of this tube is closed, and contains a certain volume of 

 dry air maintained at a constant temperature, while the 

 other end is open to the air. The instrument being accu- 

 rately adjusted by means of a mercurial plunger connected 

 with the bottom of the U-shaped tube, so that the petroleum 

 is exactly on a level in the two branches of the tube, it is 

 found to be so extremely sensitive that the slightest varia- 

 tion of the atmospheric pressure is shown by the alteration 

 of the relative level, and the amount of this alteration can 

 be measured with the greatest precision. 



CONVENIENT FORM OF MERCURIAL BAROMETER. 



A mercurial barometer especially convenient for travelers 

 has been invented by Staif Commander George of the British 

 Marine, and is described by Dr. Gurt, according to whom its 

 convenience as well as its excellence consists essentially in 

 the fact that it is filled anew at every station at which it is 

 to be used. The great objection to filling the barometer 

 tube consists in the difficulty of removing every particle of 

 air from the quicksilver in the tube, and securing a perfect 

 vacuum. The operation of boiling mercury is both difficult 

 and hazardous unless the method adopted by Wild be em- 

 ployed. Commander George's method of removing every 

 bubble of air consists in first introducino- into the tube a 

 string of cat-gut, on the end of which a feather is fastened, 

 which should reach to the bottom of the tube. Tlie tube is 

 then filled to one third of its height with quicksilver, which 



