86 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



a result that may, perhaps, be considered as entirely in agree- 

 ment with the deductions of Buchan, based upon the baro- 

 metric charts prepared by him. Monatsbericht Berlin Acad., 

 Feb., 1874, 118. 



A VEEY DELICATE BAROMETER. 



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 accurately ad- 

 justed by means of a mercurial plunger connected with the 

 bottom of the U-shaped tube, so that the petroleum is exact- 

 ly on a level in the two branches of the tube, it is found to 

 be so extremely sensitive that the slightest variation of at- 

 mospheric pressure is shown by the alteration of the level, 

 and the amount of this alteration can be measured with the 

 greatest precision. 12 A, XL, 55. 



THE PENETRATION OF COLD INTO THE EARTH. 



From observations on the temperature of the surface of 

 the earth which have been made regularly at the Botanical 

 Gardens at Paris, by the Messrs. Becquerel, by means of the 

 electric thermometer invented by them, some interesting con- 

 clusions have been deduced. Their observations have been 

 extended to the depth of one hundred and seventeen feet; 

 but most attention has been paid to that portion of the 

 earth nearer the surface. With reference to the penetration 

 of cold into soils of similar character, but one of which is 

 bare and the other covered with grass, while both are cov- 

 ered with snow, the observations have shown that when the 

 temperature of the air sinks from zero to 12 Centigrade, the 

 temperature of the earth at the depth of twenty inches never 

 sank to zero under the grass-covered earth, while it sank at 

 the same depth to 5 under the bare surface. From these 

 observations Becquerel makes the practical suggestion that 

 if in a sandy soil we desire to cultivate plants whose roots 

 suffer from frost, we must cover the soil with grass-sod ; and, 

 for similar reasons, if we desire to preserve vegetables or 

 other products during the winter under the soil, and secure 



