ON THE THREE REPORTS OF THE LIVERPOOL COMPASS COMMITTEE. 87 
Report on the three Reports of the Liverpool Compass Committee and 
other recent Publications on the same subject. By ARCHIBALD 
Smiru, M.A., F.R.S., and Freperick Joun Evans, R.N., F.R.S. 
Tne task which we have undertaken, at the request of the British Asso- 
ciation, is in some degree lightened by the publication, since the last 
meeting, of the ‘ Admiralty Manual for ascertaining and applying the De- 
viations of the Compass,’ a work which has been compiled under our joint 
editorship, and published by the direction of the Lords Commissioners of the 
Admiralty. The publication of this work allows us to treat as known, 
various methods and formule which had not previously been published, and 
to which it will be necessary to refer in the sequel. It, however, makes it 
necessary that we should give some account of our own work, and this we 
think it will be most convenient that we should do at the outset. 
The ‘Manual’ is divided into four parts. Part I. contains the well- 
known “ Practical Rules ” published by the Admiralty, drawn up originally, 
in 1842, by a committee consisting of the late Admirals Sir F. Beaufort and 
Sir J. C. Ross, Captain Johnson, R.N., Mr. Christie, and General Sabine. 
These rules were, and still are, purely practical,—the object being to enable 
the seaman, by the process of swinging his ship, to obtain a table of the 
deviations of his compass on each point, and then to apply the tabular 
corrections to the courses steered. 
Part II. is a description of the valuable graphic method known as 
*Napier’s method,” in which the deviations of the compass are represented 
by the ordinates of a curve, of which the “courses ”’ or azimuths of the ship’s 
head which correspond to the deviations are the abscisse. These azimuths 
may be measured either from the “correct magnetic north,” in which case 
they are called the “correct magnetic courses,” or from the direction of the 
disturbed needle, in which case they are called “ compass courses ;”’ and we 
should in general obtain one curve if the abscisse represent one set of courses, 
and a different curve if the abscisse represent the other set. It was, we 
believe, first observed by Mr. J. R. Napier that, by drawing the two sets of 
ordinates in proper directions, each may be made to give the same identical 
curve, and, conversely, that the same curve may be made to give the devi- 
ations as well on the correct magnetic courses as on the compass courses, 
with the additional advantage that the one set of courses may be at once 
derived from the other by going from the axis of abscisse to the curve, in a 
direction parallel to one of the sets of ordinates, and returning to the axis 
of abscissee in a direction parallel to the other. The original direction of 
each set of ordinates is arbitrary, the scale, however, depending on those 
directions. By drawing the ordinates at angles of 60° and 120° from the axis 
of abscissee, we have the advantage that the scale along each axis of ordinates 
and also along the axis of abscisse is the same; and these directions are in 
general the most convenient, although in particular cases, as when the 
deviations are very small, it is convenient to take a larger scale for the ordi- 
nates than for the abseisse. The practical advantages of the method are 
very great. It enables the navigator, from observations of deviations made 
on any number of courses, whether equidistant or not, to construct a curve 
in which the errors of observation are, as far as possible, mutually compen- 
sated, and which gives him the deviation as well on the compass courses as 
on the correct magnetic courses. Various modifications of this method have 
been proposed, of which one by Capt. A. P. Ryder, R.N., deserves particular 
mention from the facility with which it may be used by those to whom the 
