44 



It consists of a cylinder A, on which the recording paper is 

 wound, revolving once a week by means of a clockwork contained 

 inside. A series of corrugated metallic shells B, eight in number, 

 joined one above the other and exhausted of air, forms an aneroid 

 system eight times as sensitive as a single chamber. The movement 

 of the shells is still further greatly magnified and is transmitted to 

 the recording pen C by a series of connecting levers. The pen may 

 be released from contact with the paper by pushing the lever D to 

 the right. 



The corrugated shells are the same as used in ordinary aneroids, as 

 described in paragraph 46, the steel springs for distending the shells 

 being placed inside. The shells are made into a vertical column by 



Figure 28. — Richfird's aneroid barograph 



screwing the one on the other. The lower base of the column being 

 fixed, the upper end rises and falls with every variation in the atmos- 

 pheric pressure, by a quantity which is the sum of the displacements 

 of the elementary shells. 



The compensation for temperature is accomplished by leaving a 

 sufficient quantity of air in one of the shells, ascertained by experi- 

 ment when the instrument is made, so that with a rise of temperature 

 the tendency of the barometer to register too low on account of the 

 weakening of the springs, and the expansion of the levers and other 

 parts, is counteracted by the increased pressure of the air in the shell. 

 However, the instrument should be kept at a uniform temperature 

 as far as possible. 



