180 Mr. T. H, Blakesley on some Facts connected with 



in actual coincidence or in decimal relation is most striking. 

 The failure to introduce to any great extent the metrical 

 measures of length into England as against the inch is a well- 

 known case. Again, the horse-power and the erg per second 

 are not decimally related. 



So inconvenient is this last defect in the department of 

 electromechanics, that Mr. Preece has suggested that engi- 

 neers should give up the H.P. of James Watt and adopt in 

 its stead 1000 watts. This suggestion has not, so far as I 

 know, met with any support, perhaps because the modifications 

 in the definition of the unit which would be necessary for its 

 clear appreciation from a mechanical engineer's point of view 

 have not been clearly stated. The evil implied in the sug- 

 gestion is, however, great ; and, if possible, something ought 

 to be done to assuage the acute suffering which engineers feel 

 in passing from H.P. to watts. 



I think it will be conceded, too, that even the more har- 

 dened physicist feels some pangs of passage on the troubled 

 sea of transformation from the terra jirma of the Electrostatic 

 system to that of the Electromagnetic ; and I do not think a 

 rapid answer could be given by many persons to the question. 

 What is the value, in C.G.8. electrostatic units, of a cur- 

 rent of (say) 33"3 practical electromagnetic units ? Yet in 

 following out the experiments of Dr. Hertz, Avith which Mr. 

 Tunzelmann has made us familiar, such a calculation must, I 

 think, be made. 



I will here give two formulae, which will enable any mag- 

 nitude given in one system to be brought into the other. 



Let k = the exponent of I in electromagnetic system, 



'I- ^^ >j )) ^ _ » }} }} 



n = „ „ Z in electrostatic system, 



? ^^ J? >5 ^ 5J JJ V 



for any kind of magnitude brought into due correlation 

 with others. 



Then, to reduce between practical (quadrant-volt-second) 

 units electromagnetic, and C.Gr.S. units electrostatic : 



1 practical unit = s^-^io'""""?-* electrostatic C.G.S. 



To reduce between C.G.S. electromagnetic and C.G.S. elec- 

 rostatic : 



1 C.G.S. electromagnetic unit = on-h-^^iKn-mnih-q) ^^^^_ 

 trostatic C.G.S. units. 



The 3 in these equations is meant as a sufficient approxima- 

 tion to the number 2*998, which is one tenth of "v" in 

 quadrants per second. 



