594 Dr. fotherg ill's Account of 
phyfics yet undifcovered. With this view he planned 
and executed the machine, defcribed at the end of this 
relation. 
His firft attempt, however, was much fmaller; a few 
bars were laid in the due courfe of the magnetic flux, 
and impregnated by conflant attrition. To thefe other 
bars were added fucceffively, after they had been im- 
pregnated, both by the force he could give them by attri- 
tion, and what he could derive from the preceding flock 
collected in the bars. To thefe he added flill frefli bars, 
till he had formed the whole mafs as it is now prefented 
to you, and reiling on wheels and pivots, in fuch manner 
as to be eafily manageable for the purpofe of impreg- 
nating the needles he was employed to fee prepared, for 
the fervice of government, and others, who had gene- 
rofity enough to think, that the compafs, on w r hich de- 
pended the lives of the fhip’s crev r , could not be made 
too perfect, and that it deferved a reafonable compenfa- 
tion. It is to the doctor’s ingenuity and indefatigable 
attention to this ufeful inflrument, that it has acquired 
amongil us a degree of perfection unknown to our pre- 
decelfors. 
When the machine was compleated, he flill was 
adding continually to its power. He impregnated every 
lingle bar of which it is compofed, by repeated attritions, 
and applied it to the remaining bars in their magnetic 
pofition. After this operation, he always found its effi- 
cacy, for a feafon, coniiderably diminifhcd ; for the efflu- 
via 
