48 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



cally plane Circular M4/rror,of 12 inches diameter, figured by Clark, 

 which by the ordinary clock-work of the Equatorial becomes a Fahr- 

 enheit heliostat, used with certain apparatus employed iu recent so- 

 lar physical investigations, and -which is too heavy to be attached to 

 the telescope. By the simple introduction of a change wheel in the 

 clock, it is also used as an August heliostat, giving a fixed horizon- 

 tal beam. 



A Transit Instrument, by Trouguton & Simms, of London, is used 

 in connection with a Chronograph, and with a Sidereal Clock, con- 

 structed by FRODsriAM, of London, for time determinations. Two 

 Clocks, by Howard, of Boston, and two Chronometers, by Frodsham, 

 are used to indicate mean solar time. The clocks and one of the 

 chronometers have break-circuit electrical attachments, by which 

 automatic time-signals may be sent over the telegraph lines. A 

 Thomson Galvanometer, a large variety of Thermopiles, and a Casse- 

 grainian Reflector, of G^ inches aperture, without clock-work, made 

 by Calver, are used for special investigations in heat. 



3d. Daily star-observations for time are taken in order to furnish 

 a standard for the use of several trunk-railway lines, the city of 

 Pittsburgh, and various private parties. Though not the first observ- 

 atory in this country to furnish time-signals, it seems proper that 

 the statement should be made that the Allegheny Observatory was 

 the first to introduce the system, and even the name, of public " Time- 

 service " on the present extended and systematic scale, by whicb it is 

 now distributing time daily to many thousaud miles of railway (of 

 which it is the official standard), as well as to cities and individuals, 

 an example which is now being followed by others. 



The daily direct telescopic study of the solar surface is one of the 

 principal objects of this institution. It has been somewhat inter- 

 rupted during the past year by the general absence of any notewor- 

 thy features at this period of minimum of sun-spots. 



A considerable time has been devoted to spectroscopy, and partic- 

 ularly to the study of the less refrangible portion of the visible spec- 

 trum. The latter work was interrupted during a portion of July 

 and August by the absence of the director, who observed, from the 

 top of Pike's Peak, Col., the total solar eclipse of July 29. 



4th. Investigations in solar physics form the special work of re- 

 search of this observatory. During the ensuing year researches sim- 

 ilar to the foregoing will be prosecuted. A portion of the fund be- 

 queathed by Count Rumford for aiding investigations in radiant 

 energy has been placed in the director's charge, as well as an appro- 

 priation from the Bache Fund, made at the instance of the late Pro- 

 fessor Henry, and will be used during the coming year in furthering 

 the study of the distribution of energy in the spectrum. In a por- 

 tion of these researches it is proposed by the director to try the ex- 



