TRANSACTIONS OF SECTION A. 589 



Mancliester would have to put into one scale of hia balance 101*902 gram weights 

 (with small corrections for his height over the sea, and for the air displaced by the 

 weights) in order to urge this scale downwards with precisely that force (the 

 hyper-hektogram) which, if it acted on a mass of one kilogram, would generate in 

 it an acceleration of one metre per second per second. This he would express by 

 saying that the hyper-hektogram (that member of the series of decimal systematic 

 forces Avhich ditiers but little from the gravitation of a hektogram) is in reality the 

 gravitation at Manchester of 101-902 gram weights, weighed in vacuo and at the 

 level of the sea. 



Another affix which will be found convenient is -ein, meaning ' unit of,' so that 

 the forceiu shall signify the unit of force, the massein the unit of mass, &c., which 

 we happen at the time to be employing. Thus in the C.G.S. system 



The massein is one gram ; 



The lengthein is one centimetre ; 



The timein is one second ; 



whence 



The forcein is the C.G.S. dyne, which is one hyper-milligram, and 

 The energein is the C.G.S. erg, which is the hundred-thousandth part of 

 one hyper-grammetre. 



The dyne is far too small a unit of force for convenient use in the laboratory 

 of the mechanician or even of the physicist. It is the gravitation of a tiny fragment 

 of note-paper not more than about one-eighth of an inch square. And the erg, the 

 unit of energy in C.G.S. measure, is still more preposterously small. The gram- 

 metre is already a small mea.iure of energy, the hyper-grammetre is only about 

 two per cent, more ; and the err; ti the hundred-thousandth part of this small 

 measure. 



Much better systems for practical use are the K.M.S. system and the M.M.S. 

 system. The K.M.S. system, which is based on the kilogram metre and second, 

 will be found the most convenient in the laboratory of the dynamical physicist. 

 In this system — 



The massein is one kilogram ; 

 The lengthein is one metre ; and 

 The timein is one second. 



These are its fundamental units, whence are derived — 



The velocitein of one metre per second, about an ordinary walking pace ; 

 The densitein of one gram per litre, in which unit the maximum density of 



water is 1,000, and the density of standard air is 1'276 ; 

 The forcein of one hyper-hektogram, a measure of convenient amount ; and 

 The energein of one hyper-hektogrammetre, which is equally convenient. 



The supply of this amount of energy per second is what electricians call a 



' watt.' 



To the engineer and to the electrician the M.M.S. system offers certain advan- 

 tages over that just described ; and either of them is immeasurably to be preferred 



To each of these add one milligram for every 30^ metres (100 British feet) that 

 the station is above the sea, and add between 15 and 16 milligrams if the weights 

 are used in air, and if they are brass weights. 



The correction for latitude may be made with sufficient accuracy within the 

 British Isles by allowing one centigram for every 1° 7' that the station is north of 

 the latitude of 45°, i.e., one milligram for a difference in latitude of 67 minutes of 

 arc ; the error of this approximation amounting to only one milligram at Edin- 

 burgh, where it is more than at any other of the above stations — an enor which is 

 usually of no account, since no determination of the kind can be made to within less 

 than a fifthet of its entire amount. 



