TEERESTRIAL MAGNETISM. 405 



For the purpose of making the most exact magnetic sui'vey the best 

 equipment of instruments consists of the well-known unitilar magneto- 

 meter, with fittings for observing the declination, and a Bari'ow dip 

 circle. To some travelers these instruments might be found too 1)ulky, 

 and in some regions too delicate, as well as heavy to carry. 



Of suitable instruments made abroad, those used by M. Moureaux 

 in his surve}^ of France may be mentioned, as they are of similar 

 type, but much smaller and lighter than tlie instruments above 

 mentioned. 



Another form of instrument used for observing both the inclination 

 and total force is called an "L. C." instrument. Originally designed 

 for observations on board ships at sea, where the ordinary magnetic 

 instruments above mentioned are immanageable, it lias also been found 

 to give satisfactor}^ results in a land survey, where greater accuracy 

 is expected than at sea. Thus, during a series of observations extend- 

 ing from the north side of Lake Superior to the southern part of Texas 

 last year, comparisons were made between the results obtained with an 

 L. C. instrument and those of the regular unitilar magnetometer and 

 dip circle, when the agreement was found satisfactory. 



I am therefore of the opinion that a traveler furnished with a the- 

 odolite for land-surveying purposes, but fitted with a reversible mag- 

 netic needle, can at any time he observes a true bearing obtain a 

 trustworthy value of the declination. Dismounting the theodolite from 

 his tripod, the latter will serve for mounting an L. C. instrument with 

 which to observe the inclination and force. Thus, by adding to his 

 ordinary equipment an instrument weighing in its box about 21 pounds 

 he can obtain valuable contributions to terrestrial magnetism and at 

 the same time give useful assistance to geological investigations. 



CONCLUDING REMARKS. 



Although a great subject like terrestrial magnetism, even to exhibit 

 our present knowledge of the science, can not be brought within the 

 compass of an address — for it requires a treatise of many pages — 1 have 

 brought some of the broad features of it before the section in order to 

 show its connection with geography. 



I also entertain the hope that geographers will b(>comc more inter- 

 ested in a subject so important to pui-e science and in its practical 

 applications, and that it will become an additional subject to the instruc- 

 tion which travelers can now obtain under the auspices of the Royal 

 Geographical Society in geology, botanv, zoology, meteorology, and 

 surveying. 



There is a wide field open to ol)servers, and w here results often 

 depejid so nuich upon locality we require to explore more and more 

 with the magnetic needle. To look over the great oceans and think 

 how little is being done for terrestrial magnetism is a great matter for 



