Royal Astronomical Society. 323 



of others, either to the first idea or to the subsequent steps of the 

 invention." fl.ti3 vsm Jnsmal^ §ftir>i,er{-t«jTi?j. s/ii /loiriY^'m ^sojsqe to 



Description ttf tile Appgiratus for observing Transits, b^riiei^ii^ of^ 

 a Galvanic Current, now used at the Observatory of Cambridge, 

 U.S. By Mr. G. P. Bond*. 



The apparatus exhibited to the Society, is the same w^hich has 

 been for some time past in use at the Harvard Observatory, U.S., 

 and is the property of the United States Coast Survey. It consists 

 of an electric break-circuit clock, a galvanic battery of a single 

 Grove's cup, and the spring governor, by w^hich a uniform motion 

 is given to the cylinder carrying the paper. 



The electric clock is of the form proposed by Mr. Bond. Though 

 different in its object and construction, the effect produced is the 

 same with that of the clock proposed by Professor Wheatstone, 

 namely, the interruption of the galvanic circuit at intervals of a 

 second. The pallets and the escapement wheel are insulated, both 

 from the pendulum and from the other wheels. When the battery 

 is in connexion, the circuit is broken by the pallet leaving the tooth 

 of the wheel, and is restored at the instant of the beat of the clock, 

 which is in fact the sound produced by the completion of the con- 

 tact restoring the circuit ; the passage of the current being through 

 the pallet and the escapement wheel alone. With the exception of 

 the connecting wires, and the insulation of some parts, the clock is 

 like those in common use for astronomical purposes. 



Two wires pass from the clock, one direct to the battery, and 

 the other, through the break-circuit-key used by the observer, and 

 through the recording magnet, back to the battery. The length of 

 wire is of course immaterial. 



The magnet, with a slight difference in the form of the armature, 

 is the same with those used on Morse's telegraph lines in the United 

 States. The armature carries a glass pen, supplied with ink from a 

 small reservoir. Under this pen the paper revolves on which the 

 records are made. The breaking of the circuit by the clock, every 

 second, is marked by an offset made by the pen, and the breaking 

 of the circuit by the observer, is similarly recorded between the 

 second marks of the clock. The paper is wound upon a cylinder, as 

 suggested by Mr. Saxton of Washington. Unless a motion per- 

 fectly uniform is given to the cylinder, the second marks at the end 

 of an hour, instead of being arranged in regular straight lines upon 

 the paper, will change their relative positions, and the record become 

 so confused as to make it a most serious undertaking to read off the 

 observations after they have been taken. 



To give a uniform motion to this cylinder has been the chief 

 obstacle in the way of the application of electro-magnetism to prac- 

 tical astronomy, so that it should be of general utility ; for although 

 very rude contrivances will illustrate the process, and even afford 

 accurate results, the time required to interpret the record may be 

 greater than that required to make the observations throughout by 



* This is the substance of a lecture dehvered by Mr. Bond; in V<r6i<i6 tlfe 

 whole modw* operawf^* was clearly shown. -ic/ ,. ^ .' ; ti'HiiiiU; 



