43 



L-formed armature, and is also partly lifted by the pull of a spring 

 carried wholly on the armature. The outer end of the long arm is 

 tipped with a bit of soft rubber, and is further loaded with a small 

 counterweight, which rests lightly on a small post or stop provided 

 for that purpose. 



86. The action of the marker is as follows : When the armature is 

 suddenly pulled down upon the magnet the rubber-tipped rod is 

 thrust forward against the rim of the large wheel. The inertia of 

 the counterweight suffices to overcome for an instant, but only for 

 an instant, the pull of the spring previously mentioned. In this 

 instant, however, the rubber-tipped end of the rod has engaged the 

 rim of the wheel and the slower-acting pull of the spring then lifts 

 the rod and thus turns the wheel a small distance (one to two tenths 



FiGDEB 27. — Time marker 



of an inch). As soon as the armature is released by the breaking of 

 the contact in the clock, the wheel and float are released and oscil- 

 late freely for a moment, producing the results already fully 

 explained. 



87. The recording drum makes a complete rotation in T4 hours, 

 i. e., 3 days and 2 hours. Sheets ordinarily are changed at any time 

 between 11 a. m. and 12 noon, preferably shortly after 11 a. m. 

 The new record is therefore fully started before noon, and a check 

 reading of the standard barometer is made as nearly as possible at 

 noon. This furnishes a check observation for determining the start- 

 ing error of the barograph. Further checks may be obtained sub- 

 sequently from the regular observations at 8 a. m. and 8 p. m. 



88. Aneroid harographs. — Extremely simple and portable baro- 

 graphs are constructed upon the aneroid principle, of' which that of 

 Richard, being widely used, is fully described. (See fig. 28.) 



