WE is the equinoctial, P its pole,
KL is the ecliptic, K its pole,
ESWN is the horizon, Z its pole ;

PXX is the circle of declination passing through X,
is the circle of latitude passing through X,

KXk

ZXa

is the circle of altitude passing through X;

is the right ascension and xX the declination of X, is the longitude and kX the latitude of X,

is the azimuth and aX the altitude of X.

II. EXPLANATION OF THE POLAR CO-ORDINATES FOR THE SURFACE OF THE CELESTIAL SPHERE.

The projection is on the horizon.

NPZS is the meridan,

PXx the hour circle passing through X; then the angle QPx is the hour angle of X,

the arc PX is the polar distance of X.

This figure illustrates also other elements connected with the diurnal motion of the heavenly bodies.

EZW is the prime vertical,

E is the east point, W the west point,

Ee or Ww is the amplitude of X.

The annexed projection on the horizon illustrates the definitions relating to diurnal time.

NPQS is the meridian,

Pr the hour circle passing through the first point of

Aries,

PXx the hour circle passing through the centre of the

actual sun X,

PM the hour circle passing through the mean sun

M;

CONCLUSION.

WE purposely refrain from giving a complete classification of the definitions in navigation. There is nothing that would do a student more good than to make this for himself after he has had a proper model placed before him. If we have furnished such a model we have effected our object. By the application of the simple principles we have exemplified, and the information easily obtainable by the alphabetical arrangement of the Glossary of Navigation,' the young navigator will be able to lay a solid theoretical foundation for his professional knowledge.

H.M.S. "IMPLACABLE," June 1865.

Lately published,

A GLOSSARY OF NAVIGATION:

CONTAINING

THE DEFINITIONS AND PROPOSITIONS OF THE SCIENCE,

AND DESCRIPTION OF INSTRUMENTS.

BY THE

REV. J. B. HARBORD, M.A., R.N.

St John's College, Cambridge; Chaplain and Naval Instructor.

In post 8vo, with Engravings, 6s.

OPINION S.

Captain A. C. KEY, R.N., C.B., Captain-Superintendent of
the Royal Naval College.

I think it well adapted for young naval officers, and likely to be of good service to them during their studies; it has also filled a place among navigation books that was much needed.

Rev. T. J. MAIN, M.A., F.R.A.S., Professor, Royal Naval College.

I should be glad to find it extensively used by young naval officers, because we find them very deficient, for the most part, in the knowledge of the definitions in Navigation and Nautical Astronomy, a defect which this book is admirably calculated to correct.