FeatJiers of Birds y mde'pertdent qfMoultingi 
of feathers, all of which are white ; and that the coloured fea- 
thers at the same time change to white. In spring, most of the 
white feathers drop off, and are succeeded by coloured ones ; 
or, I rather believe^ all the white ones drop off, and that they 
get an entire new set. At the two seasons they change very 
differently ; in the spring, beginning at the neck, and spreading 
from thence ; now, they begin on the belly, and ^nd at the 
neck. There are also ptharmagans in this country, which are 
in all respects the same as those I have killed on some high 
mountains in Scotland.” Vol. i. p, S78. 
Art. XI. — On the Proper Method of laying down a Ship's 
Ti'aclc on Sea Charts y with some Remarhs on the Importance 
of Time-Teeepers in Navigation. By Captain Basil Hall, 
R.N. F.R.S. Lond. & Edin. Communicated by the Author. 
There is no point in practical navigation of more impor- 
tance, than the allowance for the direction and velocity of 
currents ; and although the introduction of time-keepers and 
lunar observations has led to much more accurate methods of 
making this estimate, yet there is unquestionably still much ob- 
scurity belonging to this branch of the subject. And although 
it is scarcely to be hoped that we shall ever arrive at a correct 
knowledge of the laws which regulate the great streams of the 
ocean, we may certainly hope to approach much nearer than we 
are at present to the true state of the facts, and that we shall 
eventually be able, in the practice of navigation, to make much 
juster allowances than we now do for the influences of these 
powerful agents. 
Probably much of the obscurity which belongs to this sub-*^ 
ject, arises from the inaccurate way in which the tracks of ships 
exposed to the influence of currents have been laid down on our 
charts ; for the method most in use has this essential defect, 
namely, that on inspecting the chart of a preceding navigator, 
it is rarely possible to discover where any current began, where 
it ceased to act, what was its direction, or what its velocity, — 
ail essential points. 
