89 



a scapement which, after the experience of a century and a half, 

 still holds the first place with astronomers ; 



2. The chronograph, in which he carried out the views of 

 Mr. Bergin; and 



3. The apparatus which he applied to the pendulum of the prin- 

 cipal clocks of the Armagh Observatory. 



In the first of these the pallats must combine extreme hardness 

 with perfect truth, especially on the cylindric surfaces from which 

 the scapement derives its peculiar properties. By a simple applica- 

 tion of the revolving lap, which when seen is self-evident, he con- 

 structed them, even in hard steel or sapphire, with almost mathe- 

 matical truth. 



Tn the chronograph the task required was to trace on an uni- 

 formly revolving disc a spiral line, which could be dislocated during 

 the continuance of any phenomenon, and thus preserve a graphic 

 record of the time on a highly magnified scale. 



A little before his death Mr. Sharpe was engaged by Mr. Cooper to 

 combine this principle with the conical pendulum, and would proba- 

 bly have made an instrument capable of being applied with singular 

 advantage to the electro- telegraphic mode of observation, recently 

 invented in America. 



The third was intended to obviate a defect which Dr. Robinson 

 suspected to exist in the means of connecting a pendulum with the 

 wheel-work which maintains its motions. This is done in general 

 by a crutch connected by its arbor with the pallats, and at its ex- 

 tremity driving the pendulum rod ; the axis of that arbor should 

 be in the same line with the centre of the pendulum's rotation, but 

 this condition can neither be certainly fulfilled nor verified. Mr. 

 Sharpe joined the rod and crutch by a spring resembling a flattened 

 figure of 8, which is of scarcely appreciable elasticity in the ver- 

 tical direction, but so rigid in the horizontal that it transmits undi- 

 minished the full power of the train. 



Mr. Sharpe died at his house in Dublin on the 13th of April, 

 1850, at the early age of thirty -one. 



5. Rev. Nicholas John Halpim, elected a Member of the Academy, 

 10th February, 1845. He was born 18th of October, 1790, at Portar- 

 lington, in the Queen's County. He entered Trinity College, Dub- 



