68 Description of a Printing Chronograph. 



motion ; especially is this true for the fast-moving wheel. 

 After a long series of experiments, during which the fast- 

 moving wheel was detached and stopped in various ways, 

 we finally made the impression from the spring of the 

 hammer only ; not allowing the blow to fall directly on 

 the type, but arresting it about half an inch before it 

 reached the top of the type. By this device, which is re- 

 garded of the greatest importance, the motion of the type 

 is not disturbed an appreciable amount. Any number of 

 impressions following each other in rapid succession does 

 not disturb the fast-moving wheel the one-hundredth part 

 of a second. By this plan, none of the type- wheels are 

 stopped, or locked in the act of printing, and records. of 

 observations may follow each other as fast as the hammer 

 can be made to deliver the blow. 



If the record is made while the type-wheel indicating 

 integer seconds is in the act of escaping, two numbers, or 

 one number and part of another, is printed, so there is 

 never any ambiguity about the record ; this condition, of 

 course, only occurs when the fast-moving wheel indicates 

 0.95 to 0.00 sec. If two numbers are printed when, for 

 example, the hundredths read 98, the smaller of the in- 

 teger seconds is the correct one. The time required for 

 the action of the escapement is about 0.06 sec. 



The blow for printing may be struck directly, by means 

 of a strong electro-magnet ; but the cost and trouble of 

 keeping up a large battery for this purpose led us to do all 

 the work mechanically, only using electricity as the go- 

 verning power. Accordingly, a heavy running gear was 

 built for raising the hammer, capable in its present form 

 of delivering 2,000 blows without winding ; and it can be 

 readily modified to give five times that number, if desirable. 

 This gearing is entirely detached from the hammer when 

 elevated, but is unlocked just before the hammer reaches 

 the type, immediately raising it again. The time con- 



