1871.] Electricity. 431 



the inventor, or rather adapter, M. Poisset, says is apparent only, and has 

 been combated in Professor Hughes's type-printer. 



A modification of Steinheil's telegraph has been brought out by Mr. Herring. 

 It is furnished with two keys, one to work a lever carrying a pin, to make a 

 dot, and the other to work a lever carrying a small linear style, to print a dash. 

 Greater accuracy seems likely to be secured, for it takes a long time to acquire 

 the art of releasing or holding down the Morse key the proper interval, and 

 generally learners find it easier to manipulate the single-needle than the 

 Morse. It would also appear that increased speed is obtained, since the dash 

 is printed in equal times with the dot. Mr. Herring suggests that it would be 

 practicable to emboss two slips at the same operation, and to give one to the 

 sender, who would thus know with certainty what messages had been dispatched. 

 The instrument would be especially useful as a record in a single-needle or 

 a bell circuit. 



Mr. C. W. Siemens, F.R.S., in an interesting paper, read before the Royal 

 Society, on " The Increase of Electrical Resistance in Conductors with Rise 

 of Temperature, and its Application to the Measure of Ordinary and Furnace 

 Temperatures ; also a Simple Method of Measuring Electrical Resistances," 

 showed that, according to the principle of the increase of resistance in a con- 

 ducting wire with increase of temperature, an instrument could be constructed 

 for measuring with extreme accuracy the temperature at distant or ordinarily 

 inaccessible places, such as the top of a mountain, or the interior of a furnace 

 where metallurgical or other operations are conducted. To measure tempera- 

 tures not exceeding ioo° centigrade, the apparatus is so arranged that two 

 similar resistance coils are connected by a light cable containing three wires 

 insulated from each other. These coils are termed " the thermometer coil " 

 and " the comparison coil." The thermometer coil, carefully rendered imper- 

 vious to moisture, is placed in the situation of which it is desired to ascertain 

 the temperature ; and the comparison coil is plunged into a test-bath, whose 

 temperature is raised or lowered until an electrical balance is obtained between 

 the tv/o coils, as indicated by a gaivanoscope. This equality of resistance can 

 only take place when the coils are at the same temperature, — consequently the 

 temperature of the test solution, measured by a delicate thermometer, is the 

 temperature of the situation of the thermometer coil. The temperature of the 

 connecting wires between the coils, which may be some miles apart, would 

 materially affedt the correctness of the measurements, if this source of error 

 were not eliminated by means of a third wire connecting both coils of the 

 instrument. The second portion of the paper is devoted to the description of 

 an instrument for measuring electrical resistances without the aid of a mag- 

 netic needle or set of resistance coils, such an instrument being much called 

 for on shipboard, where the motion renders delicate manipulation with nicely- 

 balanced needles a matter of great difficulty. It consists of two graduated 

 voltameter tubes, so connected that the battery current is divided between 

 them, the branches including a known standard resistance and the unknown 

 resistance to be measured. From this arrangement an expression is found for 

 the unknown resistance, in terms of the standard resistance, by means of the 

 volumes of gases evolved in n arbitrary units of time. Any change of 

 atmospheric pressure affedts both tubes of the voltameter equally ; therefore 

 any error from this cause is obviated. The upper ends of the tubes are 

 closed by small weighted valves, which can be raised after each observation 

 to allow of the escape of the gases without taking the instrument to 

 pieces. Mr. Siemens has aptly termed this valuable invention " a differential 

 voltameter." 



Referring to Professor A. A. Mayer's method of fixing and exhibiting 

 magnetic curves, Mr. C. J. Woodward writes to say that a somewhat similar 

 method to the one Dr. Mayer describes is in use by Mr. W. F. Barrett, of the 

 International College. Instead of using shellac, Mr. Barrett uses a solution 

 of gum, which is allowed to dry on a pieee of glass, and when the figures are 



