324 Royal Astronomical Society. 



the old method > and the liahility to errors in the minutes and secondH 

 is increased. A saving in the quantity of recording surface was also 

 requisite. 



The apparatus invented at Cambridge for this object is called 

 the spring governor. The train of wheels which communicates the 

 motive power to the cylinder connects with a small fly-wheel. This 

 fly is for supplying momentum, and holds no part in the regulation. 

 Beyond this fly, reckoning from the cylinder, is a half-seconds 

 pendulum, with a dead-beat escapement. The connexion between 

 the escapement- wheel and the fly is through a short spring. The 

 elasticity of this spring allows the motion of the escapement-wheel 

 to be completely arrested at each vibration of the pendulum, while 

 the momentum of the fly, acting for a small fraction of a second 

 only on the spring, keeps up the motion of the cylinder. The ma- 

 chinery is thus completely under the control of the pendulum. No 

 accumulation of irregularity can take place beyond the limits of the 

 bending and unbending of the connecting spring. After this is 

 adjusted to its minimum, the continuous rotary motion will be per- 

 formed with all the accuracy of the beats of the pendulum for any 

 length of time. It is, in fact, a complete solution of the difliculty 

 of producing exact uniform motion. An advantageous application 

 of the same principle might be made to the clock-work for the 

 equatoreal motion of telescopes. 



The cylinder makes a single rotation in a minute. The second 

 marks and the observations succeed each other in a continuous 

 spiral. When a sheet is filled, and it is taken from the cylinder, 

 the second marks and observations appear in parallel columns, as 

 in a table of double entry, the minutes and seconds being the two 

 arguments at the head and side of the sheet. 



The observer, with the break-circuit-key in his hand or at his 

 side, at the instant of the transit of a star over the wire of a tele- 

 scope, touches the key with his finger. The record is made at the 

 same instant on the paper. The operation may be repeated easily, 

 at intervals between the successive transits, of one or two seconds 

 each. 



ITie experience we have now had places beyond doubt the fact, 

 that, for convenience and accuracy of individual results, this new 

 mode of observing is in advance of the old. The number of com- 

 parisons for differences of right ascension may be increased to an 

 extent which distinguishes it, equally with its superior accuracy, as 

 a real improvement in the science of practical astronomy. The 

 extension of the method to the registration of difi^erences of decli- 

 nation, simultaneously with difi^erences of right ascension, promises 

 great facility in taking zones of small stars. 



Owing to the difliculty of obtaining precise information respect- 

 ing scientific matters in America, considerable inaccuracies have 

 crept into the historical part of the lecture given by the Astro- 

 nomer Royal on the American method of observing by the electro- 

 magnetic circuit (Phil. Mag. S. 3. vol. xxxvi. p. 142). The preceding 

 note from the Astronomer Royal will prevent misconception on 

 this point. But, setting aside the claims of individuals in this 



