Polytechnic Association. 567 



365 leaves, in which the errors of eye and hand, necessarily made 

 in recording personal observations, are avoided. All these devices 

 are of the highest order of merit. A complete description of the 

 automatic barometer will be found in the American Institute Trans- 

 actions for 1865. 



A Printing Chronograph. 



By Prof. G. H. Hough, of the Dudley Observatory. 



About the year 1848, the idea of recording astronomical observa- 

 tions, by the use of galvanic electricity, was put in successful opera- 

 tion by different individuals. Since that time chronographs of various 

 forms have been constructed for recording in a legible manner on a 

 moving sheet of paper the time of any phenomenon observed. The 

 great superiority, in point of accuracy and saving of labor over the 

 old eye and ear method, formerly used, led to the almost general 

 adoption of the new plan. During the past ten years the idea of 

 constructing a chronograph, which should print with type the time 

 of the observation, has been entertained by a number of persons. 

 About five years since, Prof. Hilgard, of the Coast Survey, read a 

 description of an apparatus designed for this purpose, and about the 

 same time Prof. C. A. Young, of Dartmouth College, published a 

 proposed plan for one, in Silliman's Journal of Science. But, so far 

 as we are informed, the mechanical construction of such an apparatus 

 has not heretofore been attempted by any one. The construction of 

 a machine which shall carry a type-wheel capable of giving impres- 

 sions, with uniform velocity for a number of hours together, without 

 sensible variation in its motion, is a problem which is not easy of 

 solution. 



Some five or six years ago, in a paper read before the Albany Insti- 

 tute, I gave an account of the method I proposed to adopt, and in the 

 construction of the machine, now to be described, the plan then pro- 

 posed has been generally followed. My plan, which is radically dif- 

 ferent from any other proposed, is based on the principle of using 

 separate systems of mechanism for the fast moving type-wheel, and 

 those recording the integer minutes and seconds, regulating each with 

 electro-magnets controlled by the standard clock. For a clear under- 

 standing of the mechanism, elaborate drawings would be necessary. 

 We shall, therefore, merely give a general account of its construction 

 and peculiarities : 



I. A system of clock-work carrying a type-wheel with fifty num- 

 bers on its rim, revolving once every second ; one, two, or parts of 



