BOUGUEr's voyage to PERU. ^OQ 



I was under the neceffity, in order to atlain to a fufficient exadlltude in the con- 

 ftruftion of my map, frequently to notice the variation of the needle, and I was far- 

 ther invited to this from a convidlion how much fuch forts of experiments are intereft- 

 ing to philofophy. I remarked at Quito the magnetic needle to dip towards the 

 north nearly ten degrees below the horizon. I fay nearly, becaufe, having caufed 

 three different needles to be made of different lengths, I could not fucceed in fixing 

 them precifely to the fame incHnation* At the period the variation was found to be 

 eight degrees and a half towards the north-eaft, it was at Plata the fame the following 

 year in July ; and four months after, I found it at Saint Martha at fix degrees 

 thirty-five minutes, and always to the north-eaft. I muft notice by the way, as it is 

 fubjefl: to divers irregularities, I have frequently found portions of rocks fpread over 

 the furface of the foil, which exteriorly were black, and appeared to have been expofed 

 to the aftion of fire, and I really believe they had been thrown there by the explvjfion 

 of fome volcano. I can compare them to nothing fo properly as maffes of clay, Iplit 

 and chapped by the fun, and afterwards converted into ftone. The variation of the 

 needle differs fo much in thefe places, that you have only to advance five or fix paces, 

 and you find a difference fometimes of more than thirty degrees in the diredion of it. 

 Thefe ftones are noticed in feveral places ; but at about one third of the diftance on 

 the way from Plata to Honda, three leagues cw thereabouts from Bacche, fome re- 

 markable ones are to be found. Two of the biggeft of them have a furface of nearly 

 twenty feet in length, by eleven high ; it is very fmooth, not chipped, and upon it 

 are engraved many charaders and figures. Similar ftones equally well engraved are 

 found in places more remote and higher in the neighbourhood of the Cordelier, but 

 I have feen none of them ; I have made a drawing of the laft. They call them, but very 

 improperly in the country, painted ftones (Piedras Pintadas) ; probably fome infcrip- 

 tion is defigned by all thefe figures and chara6lers, and points out by hieroglyphics, 

 the time and circumftances <?f the eruption of volcanoes, or other events, as fome ex- 

 traordinary and fudden fwell of the river. It appears to me to have been a work of 

 much deliberation and patience ; the figures are cut two inches and a half deep at 

 leaft. The property thefe ftones have to aft fo forcibly upon the compafs, demon- 

 ftrates them to contain fome portion of iron in their compofition, but thefe pahs lie 

 very much concealed ; the interior of the ftone is white, and it is- befide of very fine 

 grain. 



I fliall take occafion, while upon the fubjed of the load-ftone, to communicate the 

 refult of fome experiments which occupied me much on my journey home. It has 

 not relation to a phenomenon that required but one examination, but a fucceflion of 

 examinations made at different places more or lefs diftant from the equator. I do not 

 intend to examine if in magnetifm the governing force is diftinft or feparable from the 

 attraftive force ; but I am aware that many perfons pretend that one of the poles of 

 the earth is much more attradive than the other, and I could not make choice in the 

 world of a more proper fituation than Quito, to work at the decifion of this queftion. 

 With this defign, I caufed to be made a long needle of copper, fufpended as a mag- 

 netic needle. I had a finall nail foldered to one of its extremities and fet upright, I 

 placed this needle horizontally upon a pivot, and to the nail juft mentioned, which 

 was vertical, I applied an ordinary magnetic needle ; and I fo contrived it, by fmall 

 counter-weights, that the whole was in exadt equilibrium, and could turn freely about. 

 It is evident that if one of the magnetic poles has more virtue than the other ; as if, for 

 example, the north pole has more force, two effefts muft neceffarily arife ; not only 

 the magnetic needle will take its ordinary diredion, but being attraded more power- 

 fully 



