Terrestrial Magnetism. 327 



observe indnstriously, and put down carefully, the results of ex- 

 periments, without any reference to artificial lines, until we have 

 dotted the map pretty thickly over with our records, and then see 

 into what forms they will arrange themselves. 



I have thus laid before your readers so much of my field notes 

 as will enable them to understand in general my mode of opera- 

 ting, and have presented to them the evidence which convinces 

 me that the results, at the time and place given, were accurate 

 within at least two or three minutes of a degree. By this means 

 1 hope to inspire that confidence which alone gives interest to 

 such researches. The papers of Prof. Loomis are well calculated 

 to draw popular attention to this very interesting subject, and we 

 hope that a science which has been considered of sufficient im- 

 portance in foreign countries to induce their governments to erect 

 observatories, supply them with instruments and observers, and 

 even to fit out naval expeditions to explore distant regions for the 

 advancement of its interests, will not soon be neglected by its 

 few votaries in this country, or be so far overlooked by the great 

 body of our community, that all encouragement to its cultivation 

 will be withheld. 



Here I had intended to bring my remarks to a close ; but on 

 reviewing them I perceive there is a possibility that some of them 

 may be understood as a censure upon my friend Prof. Loomis. 

 Nothing of this kind is intended.^ There is no difference of 

 opinion between him and myself as to the facts. It is merely 

 the manner of representing a fact which has elicited the remarks. 

 A difference exists between an artificial line and a quantity deter- 

 mined in fact ; call the one A and the other B. The question is 

 then merely, is it more expedient to assume A to be the standard 

 and mark B in error, or to assume B as the standard and mark A 

 in error ? I object to the choice which Prof. Loomis has made, 

 because it will give to most of your readers, such as are not mag- 

 neticians, the impression that both Prof. Loomis, Prof. Courtenay, 

 Capt. Sabine, myself and others, are unable to determine the dip 

 within a very great latitude of error. But Prof. Loomis did not 

 originate this mode of expressing the difference of the two quan- 

 tities ; he had the precedent established by the most able foreign 

 magneticians. It may be that conventional authority in this 

 case, as in numerous others, ought to prevail, and that Prof. 

 Loomis is right in conforming to that authority. Still we hope 



