550 Proceedings of the British Association. 



m. s. 



Longitude of landing place on Breakwater by four chronometers, 16 33.60 west, 

 Longitude of staff on Mount Wise by Trigonometrical survey,.. 16 38.1 

 By mean of four chronometers, 16 39.8 



Difference, 1.7 



Mr. Dent also reported respecting his Steel Balance Spring, coated 

 with pure gold by the electro-nietallurgic process ; also of the perfor- 

 mance of his clock, in which the impulse is given to the pendulum at 

 or near the centre of percussion. By this contrivance he proposed to 

 obviate the difficulty occasioned by the oil freezing at low temperatures. 

 The stopping, of clocks at very low temperatures had induced the As- 

 tronomer Royal to invent a new escapement, which seemed to answer 

 all the conditions required ; an addition of twelve pounds could be 

 added on to the weight of the clock, and yet a variation was produced 

 in the arc of vibration amounting to only five minutes, while an addition 

 of one pound to the weight of the ordinary Graham's escapement, 

 made a difference of fifteen minutes ; by Mr. Airy's plan there was 

 always (if the term might be used) an extra reservoir of force; keeping 

 the train of wheels always up to their work, and capable of over- 

 coming the resistance occasioned by the freezing of the oil. Mr. Dent 

 then explained the principle of his patent Compensation-balance. 



Mr. Frodsham made some remarks on the compensation-balance of 

 chronometers, and explained a new compensation-balance of his in- 

 vention. — Sir Thomas Brisbane said, that praise was due to Mr. Dent as 

 the first maker who had exerted himself to determine the difference 

 of meridians by chronometers. He had shewn, that by chronometers 

 the difference of longitude could be had with as much certainty as 

 by any other method in use, and at an expense bearing no proportion 

 to that of rockets, or any other means hitherto adopted. Dr. Robinson, 

 of Armagh, was at present engaged in a series of rocket observations 

 in Ireland. It had been the intention of Dr. Robinson to connect 

 the Irish with the Scotch observatories, and for that purpose a large 

 depot of rockets had been obtained from government, and stood in 

 Dumbarton Castle, but unfortunately the unfavourable weather in 

 spring had prevented the execution of the design, and he had received a 

 letter, within a few days, from Dr. Robinson, stating that the strong 

 twilights of the present season would make it requisite to postpone the 

 work until autumn: these facts would at once convince the Section 

 of the superior economy and saving of time to be attained by adopting 

 Mr. Dent's suggestion of chronometrical observations. — Mr. Holden 

 inquired, why the method of moon-culminating stars, which was so 



