158 
NATURE 
[ Kune 30, 1870 
of the sky, written of course by ascientific man (one who 
seems to have read that silly little book by Chevreul on 
complementary colours), in which he suggests that as the 
sun looks orange, “/erefore the sky looks blue. He says 
that upon this theory the planets of Sirius and Vega | 
must have a black sky, those of Betelgeuse a green sky, 
and soon. But if my readers go to the Royal Academy, 
some of them will probably be a little surprised to find 
that they are positively living on a planet which enjoys 
the advantage of a solid lemon-yellow sky ! a sort of in- 
formation not to be picked up every day. In the same 
sort of way, ethnological students may inform themselves 
that the ancient Greek heroines were shaded with streaks 
of treacle about their “great marbly limbs.” But the 
judicious investigator will take note that the chief end of 
most of this canvas, and the purpose of most of this 
paint, is to indulge the artists and their disciples with 
reminiscences of antecedent art—an exemplification of 
the cud-chewing tendencies of his species. Many of 
them have drank deeply at the fountain of second-hand 
beauty ; they have drank perhaps intemperately, and 
their speech must needs be somewhat sublime to unin- 
_ structed ears. 
Let not the student carry away the impression that 
artistic faculties and wanton inaccuracy are necessarily 
connected. If the scientific writer who offered sugges- 
tions to account for the blueness of the sky had acquired 
the habit, which the practice of painting gives, of com- 
paring the intervals between different colours, and esti- 
mating the intensities as well as the extent of the several 
elements that go to make up any given scene in the out- 
of-doors world, he could hardly fail to notice that the 
sun at mid-day would in all cases be the least coloured 
object in the whole field of view; that the colours of other 
objects would neither gain nor lose perceptibly where 
exposed to his direct rays; whereas, the shaded and over- 
shadowed parts of them would suffer various enkance- 
ments or modifications from the coloured rays reflected 
from surrounding surfaces ; and that, in the case referred 
to, in a mid-day cloudless sky, the most widely extended 
and most purely coloured of all the surrounding spaces 
being blue, all the shadows and many of the shades would 
be dyed blue, so to speak, over their own proper colours ; 
and that the whole scene would be stecped in the “blue 
flood of light” of the poets. The colours of the face of 
our planet, both native and derived, present a large field 
for study, and a good deal more can probably be ascer- 
tained about them than about many less pleasant yet less 
neglected subjects ; and when the scientific investigators 
have done with the blue sky, I hope they will let us hear 
what they have to say of the blue sea. 
What is the moral of all this? Simply that the 
scientific men pay too little attention to the broader 
aspects of the visible world ; while the artists on their part 
pass by the clear fountain of natural beauty, and content 
themselves with dreamily sipping lukewarm water from 
the corroded vessels of their forefathers ; the one group of 
doers standing apart from the other; whereas, if either 
would go to schocl with the other, they would, in my 
opinion, each stimulate and aid the labours of the other, 
and divide between them a far larger slizie of the spoils 
the world, 
JOAN BRETT 
] 
ON THE NATURAL LAWS OF MUSCULAR 
EXERTION 
MONG a multitude of profound and happy sugges- 
tions to be found in Mr. Babbage’s Economy of 
Manufactures, are some remarks on the relation between 
fatigue and the rapidity or degree of muscular exertion. 
Coulomb, it appears, had previously investigated the most 
favourable load for a porter, and had ascertained by ex- 
periment that a man walking upstairs without any load, 
and raising his burden by means of his own weight in 
descending, could do as much work in one day as four 
men employed in the ordinary way with the most favour- 
able load. Mr. Babbage clearly points out (p. 30) that 
the exertion necessary to accomplish any kind of work 
consists partly of that necessary to move a limb of the 
body, and partly of the force actually utilised in the work. 
The heavier the work done, the larger the proportion, 
therefore, of the power utilised. But there is a limit to 
this mode of increasing the useful effect, because, by the 
natural constitution of the muscles, they can only develop 
a limited amount of force in a given‘time, and the fatigue 
rapidly increases with the intensity and rapidity of exer- 
tion. Hence there is in every kind of work a point of 
maximum efficiency, which is in practice ascertained more 
or less exactly by frequent trial. 
This subject appeared to me to possess interest for at 
least two reasons : it might be made to throw some light 
upon the chemical and physiological conditions of muscu- 
lar force ; it might also point out how we could make some 
commencement, however humble, of defining the mathe- 
matical relations upon which the science of economy is 
founded. I have therefore attempted to add precision 
and certainty to the ideas put forth by Coulomb and Bab- 
bage, by some experiments of a simple kind. 
The first and least interesting series of experiments con- 
sisted in ascertaining the comparative distances to which 
various weights could be thrown upon level ground. The 
product of the weight and distance was taken: as the 
measure of useful work, and it was the object to ascertain 
according to what law this varied, and at what point it was 
amaximum. The weights employed varied from }1b, up 
to 56]bs., and were thrown as nearly as possible in a 
uniform manner and at the most advantageous angle. 
About 57 experiments at different times were made with 
each weight, or 456 experiments in all; and it was quite 
obvious that good average results were obtained, the cor- 
respondence of different sets being very satisfactory. The 
results are as below :— 
Weight 
in 507s 7 4 2 I 
pounds 
Average 
distance 
thrown 
in feet. 
A little consideration showed it to be probable that 
these numbers would agree with an equation of the form— 
r= ee 
w+ 9 
in which a = distance thrown, 
w = weight thrown, 
= constant weight representing about half 
that of the arm, F 
/ = constant amount of force exerted. 
oe 
1°84 3°70 6°86 10°56 14°61 18°65 23°05 27°15 
; 
: 
; 
| 
