1815.) the Rise and Fall of the Tide. 281 
Friction of the Water against 100 Feet, at the mean Depth of 
6 Feet. 
Feet Lbs. Lbs. Feet. Lbs. Lbs. 
1 0-3716 0:0067 11 38-630 0-8451 
2 1°4292 0:0253 12 45°684 1°0532 
3 3°1350 O-0ATL 13 53-298 1°2751 
4A 54672 0:0809 14 61°462 1-:5569 
a 84284 O°1297 15 70°180 1:S771 
6 11-991 0°1934 16 19°443 2°2382 
7 16°154 0:2767 17 89°24T 92-6420 
8 20°906 0-3805 18 99-588 30911 
9 26°238 0°5074 19 110-46 3°581T 
10 32-152 0°6618 20 121°86 41113 
From these experiments, it is evident that the resistance a body 
meets with when moving in water consists of three parts—the head 
resistance, the minus pressure, and friction. 
The shape of the solid of the least resistance is still to be ascer- 
tained, which experiments alone can determine ; though perhaps no 
shape will answer in every velocity. 
I remain, my dear Sir, 
Yours very sincerely, 
Mark BEAvFoy. 
a ET 
ArTICLE V. 
New and important Combinations with the Camera Lucida. 
By W. G. Horner, Esq. 
(To Dr. Thomson.) 
sIR, Bath, Aug. 15, 1815, 
Tue numerous inventions of Dr. Wollaston in various depart- 
ments of philosophy are marked by that precision and completeness 
which constitute the true idea of elegance. They seldom leave to 
succeeding experimenters any hope of adding an improvement, and 
are only capable of being enhanced in estimation by multiplying the 
useful purposes to which they may be applied. These remarks are 
eminently appropriate to the Camera Lucida. As a corrective of 
the erroneous decisions of the eye, or a succidaneum to the labour 
of educating that organ, the utility of this beautiful little machine 
is well known. ‘These advantages, offered by the instrument in its 
simple form, have been proved by the geologist, as well as by artists 
in miniature, landscape, and architecture ; but I am ignorant if any 
philosopher has been struck with the still more extensive uses to 
which it may be adapted in combination with the microscope and 
telescope. 
