16 MR. DARWIN ON THE BODILY TIDES OF VISCOUS AND SEMI-ELASTIC 
rough experiments of my own, the viscosity of British pitch at near the freezing 
temperature (34° Fahr.), when it is hard and brittle, is about 10 8 X 1'3 when measured 
in the same units. 
Lunar Semidiurnal Tide. 
Height of 
Height of 
High tide 
Coefficient 
Retardation 
bodily tide is 
ocean tide is 
relatively to 
of viscosity 
of bodily tide 
tide of 
tide on 
viscous nucleus 
x 10~’ u 
/ 
£ \ 
fluid spheroid 
rigid nucleus 
accelerated by 
(v x 10“’°) 
if 
multiplied by 
multiplied by 
1 / 7T 
-1 
(cos t). 
(sin £'. 
uA4 
2' 
Hrs 
min. 
Hrs. 
min. 
Fluid 0 
0 
0 
1-000 
•000 
3 
6 
46 
0 
21 
•985 
T74 
2 
46 
96 
0 
41 
•940 
•342 
2 
25 
152 
1 
2 
•866 
•500 
2 
4 
220 
1 
23 
•766 
•643 
i 
44 
313 
1 
44 
•643 
•766 
i 
23 
455 
2 
4 
■500 
•866 
i 
2 
721 
2 
25 
•342 
•940 
0 
41 
1,488 
2 
46 
•174 
•985 
0 
21 
Rigid oo 
3 
6 
•000 
1-000 
0 
0 
Fortnightly Tide. 
Day 
3. hrs. 
Days. 
hrs. 
Fluid 0 
0 
0 
1-000 
•000 
3 
10 
1,200 
0 
9 
•985 
T74 
3 
i 
2,500 
0 
18 
•940 
•342 
2 
16 
4,000 
1 
3 
■866 
•500 
2 
6 
5,800 
1 
12 
•766 
•643 
1 
21 
8,300 
1 
21 
•643 
■766 
1 
12 
12,000 
2 
6 
•500 
•866 
1 
3 
19,000 
2 
16 
■342 
•940 
0 
18 
39,300 
3 
1 
T74 
•985 
0 
9 
Rigid oo 
3 
10 
•000 
1-000 
0 
0 
I now pass on to a case which is intermediate between the hypothesis of Sir W. 
Thomson and that j ust treated. 
8. The tides of an elastico-viscous spheroid. 
The term elastico-viscous is used to denote that the stresses requisite to maintain 
the body in a given strained configuration decrease the longer the body is thus con¬ 
strained, and this is undoubtedly the case with many solids. In the particular case 
which is here treated, it is assumed that the stresses diminish in geometrical progres¬ 
sion, as the time increases in arithmetical progression. If, for example, a cubical 
block of the substance be strained to a given amount by a shearing stress T, and 
maintained in that position, then after a time t, the shearing stress, is T exp 
