514 EEPOET — 1889. 



Hysteresis evidently plays a most important function, and tlie conductor in conse- 

 quence becomes a source of heat, which varies in intensity, not only vfith the 

 strength of the current, but also with the frequency of the alternations. 



The diiference of behaviour between iron and copper is very marked in the 

 sounds they emit when transmitting alternate currents. Iron vibrates mechanically, 

 and emits loud, powerful sounds, filling the room with a roar, and increasing in 

 intensity with the frequency. The sound of copper is very slight, and only per- 

 ceptible when the ear is close to the conductor, even with the maximum current. 

 It is only what one would expect from rapid variations in emissivity under such 

 alternations. 



This vibration, eo marked in iron, has a very important bearing on the dura- 

 bility of the insulating material ; for it is difficult to conceive any material that 

 could stand such molecular disturbances without injury for any length of time. 



The general conclusion to be drawn from these experiments is that practically 

 no serious error has been made in the form of conductors so much used for alter- 

 nating-current systems, and that nothing cheaper or better has been devised than 

 a simple stranded conductor, coated with a suitable insulating coating, and pro- 

 tected outside with lead, or some impervious and strong material. 



They do not solve the question of the distribution of current density through 

 the section of the conductor, but they do show that within the range of practice 

 the total flow of energy is the same in copper conductors, whether it be urged by 

 alternate or by steady currents. 



14. .4 new Thermometric Scale. 

 By Geoege Forbes, F.B.S., and William Henry Peeece, F.B.8. 



The recent Electrical Congress at Paris has adopted the Joiile as the unit of 

 work, and the Watt as the unit of power. The following definitions were unani- 

 mously accepted. ' The practical unit of work is the Joide. It is equal to 107 

 C.G.S. units of work. It is the energy expended during one second by an ampere 

 in an ohm. 



' The practical unit of power is the Watt. It is equal to 107 C.G.S. units of 

 power. The Watt is equal to a Joule per second.' 



The Therm as the unit of heat, which was proposed by the British Association 

 Committee at Bath last year, did not commend itself to the French members. 

 They preferred for the present to retain the term Calorie, notvrithstanding the con- 

 fusion from there being two units of that name. It is said there is only one Calorie 

 in the C.G.S. Centigrade system. 



But the question arose— Is there any need for either the Therm or the Calorie ? 

 Cannot the Joule be made a thermal unit also, for the latter is only a unit of work ? 

 The heat generated in T seconds by C amperes flowing through E ohms (or driven 

 by E volts) is C'*RT = EOT Joules. If we take the mechanical equivalent of 

 heat as approximately 42,140,000 ergs, or 4-2 Joules, it means that 4-2 Joules will 

 raise one gramme of pure water at 4° C. one degree. 



We have here the true scientific mode of forming a C.G.S. thermometric scale. 

 If we take the fiducial points of freezing and boiling points of pure water at normal 

 pressure on a column of mercury as usual, and divide the distance into 420 divisions, 

 then each division is a true C.G.S. unit of temperature, and will be passed by the 

 expenditure of one Joule per gramme of water. Instead of employmg degrees of 

 temperature we can use these units of temperature, and we can replace the angular 

 symbol x° by t or 6. Thus, to raise one gramme of water from freezing point to 

 boiling point requires 420 Joules, or to raise it to boiling temperature from 62 

 units It requires 358 Joules. There would be no necessity for coefficients, and 

 calculations would be simplified. Degrees Centigrade would be simply converted 

 into these units by multiplying by 4-2, and degrees Fahrenheit by deducting 32° 

 and multiplying the remainder by 2-33. 



An objection to such a scheme has been raised by Professor Potier of Pans, and 

 it is that the mechanical equivalent of heat has not yet been determined with suffi- 



