418 THIRD REPORT — 1833. 



becoming filled, is by a quarter turn of the one now upper- 

 most cut off from communication with it, and the instrument 

 is rendered portable with the end of the tube dipping into a 

 cistern of mercury, which is perfectly secure. 



By this method Mr. Newman is enabled to make portable 

 mountain barometers with very large tubes, for sufficient room 

 can be left in the cistern to receive the mercury which flows 

 from the tube into the cistern in high situations, notwithstand- 

 ing the increased diameter of the tube. Barometers, therefore, 

 can be made and ti'ansported, which when put up may be de- 

 pended upon as standard instruments with perfect security. 



On an Instrument for measuring the total heating Effect of 

 the Suns Rays for a given time. By the Rev. James 

 Gumming, V. P. R. S., F.G.S., Professor of Chemistry, 

 Cambridge. 



It has appeared to Professor Gumming that the information 

 conveyed to us by the ordinary instruments for measuring the 

 heating power of the sun's rays is, in one respect, imperfect, 

 in as much as these instruments indicate only the momentary 

 energy of the rays : he was therefore led to devise a process 

 which should measure the total result of their action in a given 

 time. The process employed is to expose to the sun a retort 

 with a blackened bulb containing aether, and to note the quan- 

 tities of this liquid distilled over in different days. In some 

 cases, a second bulb of plain glass has been used to increase 

 the condensing surface, and the apparatus has been otherwise 

 modified. With instruments on this plan Professor Gumming 

 has registered the daily effects of the sun's radiation for more 

 than two years, and he hopes soon to publish his results in a 

 connected form. 



On some Electro-magnetic Instruments. By the Rev, James 

 Gumming, V.P.R.S., Professor of Chemistry, Cambridge. 



The instruments exhibited and explained by Professor Gum- 

 ming consisted of: 



1. A galvanometer of four spirals, similar to that described 

 in his translation of Demonferrand, (pi. v. fig. 86,) but formed 

 oi flattened copper wire with silk ribbon interposed, each spiral 

 being fixed upon a graduated slide. 



2. A Breguet's thermometer, with a conducting wire passed 

 through its axis, for the purpose of measuring either the heat 

 evolved by different galvanic arrangements in passing through 

 a given wire, or that evolved in different wires by the same 

 battery. 



