660 
McMunn at Stratford-on-Avon; in regard to 
criminal or semi-criminal children of the streets, 
from Mr. Lane at the Littlke Commonwealth in 
Dorset, we learn of the wonders wrought by a 
wise respect for the individual personality of the 
pupil. Shall we learn the lesson they teach? Or 
shall we go on blindly in the ways of the past? 
Te ERA OS 
THE “CONWAY” MANUAL. 
The “Conway” Manual: being a complete Sum- 
mary of all Problems in Navigation and Nauti- 
cal Astronomy. By J. Morgan, T. P. Marchant, 
and: was Sl Wood. Pp. yo." \(Lendon J. 2D: 
Potter, 1914.) Price 5s. 
HIS manual of navigation, as taught on 
board the Conway, gives the courses of 
instruction the cadets of that vessel go through 
to prepare them to qualify as navigators afloat. 
Quite properly the manual lays stress on the 
importance of all students being familiar with 
both plane and spherical trigonometry, as naviga- 
tion is simply applied trigonometry, and entirely 
discards all rule of thumb methods, but in teach- 
ing the cadets the method appears to be to plunge 
at once into a statement of the formulas used—the 
sine formula, etc., without indicating what is 
meant by sines, cosines, tangents, etc. Surely in 
teaching beginners it is best to make plain what 
is meant by the expressions used. 
In applying the formulas to practical navigation 
the manual adopts the method of zenith distances 
given by Marcq St. Hilaire about 1880, to the 
exclusion of all other methods. Now the method 
of position lines has been in use for nearly a 
century. When first started, the line of position 
was obtained by finding the longitude from the 
observation of the sun worked out with two lati- 
tudes some miles apart; the resulting longitudes 
gave a line on which the observer must be situ- 
ated. When it became of importance to ascertain 
the compass errors, at the time of observation, 
the system of working with two latitudes was 
abandoned in favour of calculating the true bear- 
ings of the heavenly object, together with the 
longitude; as the observer must be on a line of 
position at right angles to the bearings of the 
heavenly object observed. If two heavenly ob- 
jects were observed, in convenient positions with 
respect to each other, it is evident that the ob- 
server must be where those lines intersect, but 
even with one object only, by knowing the true 
zenith and polar distances, and the approximate 
co-latitude, the line of position on which the ob- 
server is situated can be placed on the chart at 
NO. 2330, VOL? 93 
NALORE 
[AUGUST 27, 1914 
once, and frequently by steering along that line 
an accurate landfall be made. In this problem 
the only doubtful point is the co-latitude. By 
Marcq St. Hilaire’s method an approximate hour 
angle is assumed, as well as an approximate co- 
latitude, and the true polar distance, to calculate 
an approximate zenith distance and true bearing, 
and the difference between the true zenith dis- 
tance, as observed, and the approximate zenith 
distance, as calculated, plotted along the line of 
bearing of the heavenly object, and the lines of 
position parallel to each other plotted. 
Lines of position are fully explained in Riddle’s 
“Navigation,” eighth edition, published in 1864, 
and can be obtained by the Marcq St. Hilaire 
method as well as by Sumners, or by calculating 
‘the longitude and azimuth of the heavenly body 
observed. When the sun is the heavenly object 
observed the zenith distance plan has the disad- 
vantage of not giving the longitude and line of 
position. Wiitn two stars at or near right angles 
to each other this does not apply, but even then 
the method of calculating the longitude and line 
of bearing appears quite as advantageous as the 
zenith distance method. But what appears to be 
omitted from the ‘Conway Manual” in the prac- 
tical work is all instruction relative to Dr. Ivory’s 
method of double altitudes or to lunar distances, 
though in the case of the sun’s double altitude 
given at page 74 the ship’s position can be cal- 
culated at once by Dr. Ivory’s method as ex- 
panded in Riddle’s “ Navigation,” without trouble 
and without any plotting and position iines. Also, 
in the example of star double altitude at page 76, 
although the rate of the chronometer for a period 
of eighty-five days has to be applied to obtain the 
Greenwich mean time, nowhere is the student 
warned that in such a lapse of time the chrono- 
meter may, and probably would, have altered its 
rate, and that the most convenient way of ascer- 
taining this in a ship at sea is by lunar observa- 
tions. 
It may perhaps be as well to point out 
also that in the problem on page 74, although the 
altitude at the first observation is corrected for the 
run of the ship, the latitude it is worked with is 
the approximate latitude of the ship at the first 
observation for both sets of the sun’s altitude, at 
II a.m. as well as at 9 a.m. It will be found 
that if the hour angle and sun’s bearing be ob- 
tained from the observations at 9 a.m., and the 
run of the ship be applied to that hour angle, as 
well as the elapsed time, a more correct hour 
angle will be obtained for the 11 a.m. observation, 
and the correct position got, as in the annexed dia- 
gram; where if A be the position of the ship at the 
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