84 GAUSS AND WEBER ON TERRESTRIAL MAGNETISM. 



Milan, with the magnetometer of that place, in October, 1836, 

 viz. 2-01839. 



To gain a clear idea of the Import of these numbers, the de- 

 termination and application of which have been hitherto under 

 consideration, imagine a number of small steel bars, perfectly 

 alike, and each weighing about 2h grammes, or ^ of an ounce. 

 Imagine further a balance, of which the length of the arms 

 beai-s to 1 metre the same proportion that 1 metre bears to 

 the space of descent in 1 second (204 millimetres nearly) ; sup- 

 pose one of these steel bars to be attached in a parallel direc- 

 tion to the horizontal beam of the balance, in such manner that 

 the equilibrium is not thereby disturbed. Then render all the 

 steel bars (including the one attached to the balance) equally 

 magnetic, and to such a degree that when another of their 

 number is placed vertically beneath the scale at the distance of 

 1 metre from the attached magnet bar, T(f oq^^ ^^ ^ milligramme 

 must be placed in the scale to preserve equilibrium. When 

 the magnetism of all the bars has been regulated in this man- 

 ner, place one of the bars horizontally, and at right angles to a 

 small compass needle, 1 metre from the centre of the needle 

 beneath, taking care that as the compass needle is deflected 

 from the magnetic meridian, the bar be also turned so that they 

 may preserve their rectangular position. Lastly, calculate how 

 many such bars are required that their united force may deflect 

 the compass needle 90^ ; the number of bars gives the terrestrial 

 magnetism in thousandths of its absolute measure. 



We may conceive in like manner the number which repre- 

 sents the absolute measure of the terrestrial magnetism to repre- 

 sent the number of these bars reckoned in thousands, the forces 

 of which must be united to cause, at a distance of a metre, a 

 deviation of 90°. This would require at 



Gottingen the force of . . . 1775 bars 



Munich 1905 — 



MQan 2018 — 



6. On the Advantages of the Dimensions selected for the small 

 Measuring Ajiparatus. 



Before concluding this article, we have to discuss the accm'acy 

 of which the absolute measurement of intensity with the appa- 

 ratus described is susceptible, and on what it is founded. It 

 has been already remarked, that the absolute intensity can be 



