148 ANNUAL OF SCIENTIFIC DISCOVERY. 



A NEW BAROMETER. 



A self-recording barometer, which has been termed Barometro- 

 graph, has been invented in France by M. Breqnet. It is designed 

 to furnish diagrams every 6 hours of the pressure of the atmos- 

 phere. It consists of 4 metallic boxes, the upper and lower of 

 which are curved ; these are vacuum-boxes, and are, in some 

 measure, a modification of the aneroid barometer. The registra- 

 tion is made by a revolving cylinder, which is wound by clock- 

 work, and is covered with a paper on which lamp-black has been, 

 deposited. On this paper a lever from the barometer makes its 

 traces as the wheel revolves. 



A NEW PSYCHROMETER. 



M. Becqnerel, Sen., has recently described to the Academy of 

 Sciences of Paris a new .psychrometer, so modified as to act by 

 electricity, which he regards as valuable for climatological pur- 

 poses. For the old instrument of two thermometers, the bulb of 

 one of which is dry and the other constantly moist, he substitutes 

 a thermo-electric circuit composed of iron and copper wire of a 

 diameter dependent on their lengths ; the longer they are the 

 greater is their diameter. Within this circuit there is a galva- 

 nometer provided with a short wire, and intended to show when 

 the temperature is the same at both the points where the metals 

 have been soldered together. One of these points is placed in a 

 medium, the temperature of which is lowered until the needle of 

 the galvanometer returns to zero, in which case the temperature 

 is the same at both points, this result being independent of the 

 magnetism of the needle : the only requisite condition is that the 

 zero of the scale remains unchanged in the course of the observa- 

 tion. The second point of junction is placed in the medium con- 

 tained in the aqueous vapor, the elastic force of which is to be de- 

 termined. It requires to be set right by comparing it with the 

 common psychrometer. With it he has ascertained the elastic 

 force of aqueous vapor at an altitude of three metres above the 

 surface of the soil, at the top of a tree, and at the surface of a 

 river. 



SIEMENS' AND WHEATSTONE'S ELECTRO-MAGNETIC INDUCTION 



APPARATUS. 



Last year Mr. Wilde's Magnetic Induction Machine caused con- 

 siderable stir in the scientific world, on account of the primary ex- 

 citing magnets being of so small a power and the ultimate current 

 of electricity excited by the large secondary electro-magnet being 

 of so large a volume and of so great intensity. It was soon per- 

 ^ceived that in proportion to the difference between the power of 

 the secondary magnet and the power of the primary exciting 

 magnet the driving power varied ; and that by this machine there 

 was a veritable conversion of mechanical into electrical force, 

 combined, of course, with magnetic force. Though this was not 



