Mechanics. 357 



Section G. — Mechanics. 



Mr Lassell gave an explicit account of his new method of 

 supporting a large speculum free from sensible flexure in all 

 positions. This he proposed to do, when in a horizontal posi- 

 tion, by supporting it at eighteen different points, on which 

 the weight might bear equally ; and by casting the speculum 

 with ribs, he proposed to adapt levers, that when the tele- 

 scope is elevated they might bear the weight among them, 

 and thus prevent it from disturbing the true form of the 

 speculum. 



Dr Robinson said that it appeared to him that the sugges- 

 tions of Mr Lassell would remedy the annoying evils which 

 every astronomer had to contend with. 



Mr Whitworth'*s communication on a new Duplex Turning- 

 Lathe was then made by Mr Scott Russell. The improve- 

 ment suggested not only doubled the quantity of work, but 

 did it in a much better style. 



Mr George Beattie then gave an account of his new Door- 

 spring, the motive power of which is the pressure of the 

 atmosphere. The principle of this excellent contrivance is 

 simply this— to cause the opening of the door to move an 

 air-tight piston from the closed end of the cylinder to the 

 open end ; the atmosphere then acting upon the piston, forces 

 it back, and thus closes the door. Several members expressed 

 themselves in terms of high approbation of Mr Beattie' s con- 

 trivance. 



Mr Stevenson made a statement of the result of certain 

 observations made by him on the force of the waves with 

 reference to the construction of marine works. The result 

 of the experiments hitherto made may be stated to be a force 

 of about 1^ tons per square foot for the German ocean, and of 

 3 tons for the Atlantic ocean ; the experiments from which 

 these results were obtained being made at the Bell Rock and 

 Skerryvore Lighthouses. 



Mr Swan then brought forward his communication on the 

 " Limits to the Velocity of Revolving Lighthouse apparatus, 

 causod by the time required for the production of Luminous 

 Impressions on the Eye." 



