154 ANNUAL OF SCIENTIFIC DISCOVERY. 



find 491 of the one set and 491 of the other, which agrees en- 

 tirely with M. Fizeau's estimated round number of 500. 

 Nature. 



ELECTRICAL DISCHARGE. 



Prof. Yon Bezolil, in the "Philosophical Magazine," thus sums 

 up the results of a series of experiments upon the electrical dis- 

 charge : 



'* 1. When an electrical discharge, after traversing a spark- 

 interval, is offered two paths to the earth (a short one and a long 

 one interrupted by a test-plate), with small striking distances, the 

 discharge is divided. With greater distances the electricity takes 

 only the shorter path, and even carries with it electricity of the 

 same kind from the other branch. 



" 2. If electrical waves be sent into a wire insulated at the end, 

 they will be reflected at that end. The phenomena which ac- 

 company this process in alternating discharges appear to owe 

 their origin to the interference of the entering and reflected 

 waves. 



"3. An electrical discharge travels with equal rapidity in wires 

 of equal length, without reference to the materials of which these 

 wires are made." 



NEW GALVANIC BATTERY. 



A new and important galvanic battery, invented by Bunsen, is 

 described in Prof. Roscoe's address before the British Associa- 

 tion. Only one liquid, a mixture' of sulphuric and chromic acids, 

 is employed, so that no porous cells are needed. The plates of 

 zinc and carbon can all be lowered at once into the liquid and 

 raised again at will. The electro-motive force of this battery is 

 to that of Grove (the most powerful of all known forms) as 18 to 

 25 ; it evolves no fumes in working, and can be used for a very 

 considerable length of time without serious diminution of the 

 strength of the current, so that Bunsen writes that no one who 

 has once used the new battery will think of again employing the 

 old forms. 



RESISTANCE PYROMETER. 



Mr. C. W. Siemens has invented an instrument called an 

 " Electrical Resistance Pyrometer," which will measure the heat 

 of the hottest furnace. It is based on the principle that the re- 

 sistance of pure metals to the electric current increases with the 

 temperature in a very simple ratio. A platinum wire of known 

 resistance is coiled round a cylinder of fine clay, and covered 

 with a tube of the same material. The coil is connected with a 

 Daniell's battery of 2 cells and with a resistance measurer, and 

 placed in the furnace whose temperature we wish to ascertain. It 

 is then only necessary to read olf the indications of temperature 

 on the graduated resistance measurer. 



