238 
MAGAZINE OF SCIENCE AND ART. 
As an instance of tile confusion of terms arising from 
hasty writing, in a popular Treatise on the Elements of 
Mechanism published in “Whale’s Senes,” it is stated 
at page 5, that “the power multiplied by the length oi 
its arm is equal to the weight multiplied by the length 
of its arm; the former product is called the momentum 
of the power, and the latter the momentum of the 
weight.” _ , . . - . 
Now “ momentum” is correctly defined as being the 
power or force with which moving bodies strike any 
obstacle which opposes their motion; in other words, 
momentum is represented by the weight ot a moving 
body multiplied into it aydpdttf; but the “ moment 
of a bodv is its intensity multiplied into its leverage ; 
and in the above extract from a popular Treatise, “mo¬ 
mentum’' is compounded with “moment,” and the 
student is necessarily perplexed by -this confusion oi 
te X It is to he regretted that Treatises of a popular 
nature contain, too often, assertions without reasoning, 
and propositions of the most heterogeneous nature all 
jumbled together, and which only perplex the student 
and confuse his reasoning faculties. Even Algebra 
should be discarded in such Treatises, for it is doubtful 
whether this branch of mathematics is of much practi- 
cal value. , , , , . , 
The writer wishes, however, to be clearly understood. 
He by no means wishes to depreciate the value ot ma¬ 
thematical reasoning, for it generates habits of strict 
attention, of mental discipline, and of constant reference 
to fundamental principles. In reasoning as in other 
arts, a judicious cultivation of mathematics enforces 
continuity of attention and coherence of thought, and 
it is to he regretted that there too often prevails an ob¬ 
scurity or perplexity of thought, wind, prevents men 
from 'seeing clearly the necessary connection of their 
conclusions with their premises. But the mathema¬ 
tician knows that alt must he referred to first prin¬ 
ciples, and ftows inevitably from them,-that however 
far he mav travel, ho can at will go over any portion oi 
his path, and satisfy himself that Ins conclusions are 
legitimate and his deductions correct . 
26. The name of the ilhistrions Newton, who by Ins 
prodigious gonins and power of calculation, not only 
discovered tho laws by which the whole vast system of 
tho universe, through countless ages, has been held 
together and regulated, but who also reduced those laws 
to the most perfect order and harmony, must always 
hold a station far above that of the greatest kings or 
conquerors, and the author of die “ Principle, justly 
deserves to rank among tho great benefactors ot the 
human race. In order to explain the motions ot the 
heavenly bodies, to determine by mathematical reason¬ 
ing the ratio of attraction nnd of original impulse, and 
to“shew the effects of their separate or combined action, 
Newton had not oplv to perform the most difficult cal¬ 
culations, but he had to invert new methods of calcula¬ 
tion in the highest range of mathematical science. lie 
had moreover to demonstrate, not only all the phe¬ 
nomena of falling bodies, bat also to explain every 
movement and every inequality ot movement in its 
minutest details of planetary motions, including that 
of tho sun, earth, moon, planets, satellites, comets, and 
stars, leaving not one fact imperfectly explained or at 
variance with his wonderful discovery ot the laws of 
gr ' 27 lt According to those laws all bodies tend to or en¬ 
deavour to reach the earth, and Tequire tho exertion of 
force to counteract this tendency, and every body per¬ 
severes in the same state, either of rest or of motion, 
unless it bo compelled to change that state by another 
force. This inertness of matter, otherwise called its 
“vis inertia 1 ," or power of inactivity, is that, m virtue 
of which it requires a certain effort or force to produce 
motion in matter if it be at rest, and to destroy or 
modify any motion which it may have acquired. JN ow 
this tendency of bodies to persevere m the same state, 
either of rest or of motion, may he regarded as a force, 
anil since matter is inert, a body impressed with a 
motion must persist in that motion in a straight line, 
and with uniform velocity for ever, unless some new 
force act upon it and compel it to change its state of 
motion or its velocity, for it cannot, of itself, change 
either. , , 
28. Thus, when a bail is discharged from the mouth 
of a gun, it requires a certain force to give it an im¬ 
petus greater than would bo required to continue its 
motion, and when the ball ceases to move, it is not that 
its original impulse is exhausted or spent, but that it is 
gradually overcome by tlie resistance of other forces, 
namely, the attraction of gravitation and the resistance 
of the atmosphere; and were it not for the operation of 
these invisible and combined forces, the ball would 
continue its motion for ever, because nothing would 
then intervene to destroy the primary impulse. Hence 
it may be said that motion communicates itself among 
other bodies, but is never lost ; and when it appears to 
be so, it in fact only passes from the moving body into 
other bodies which are at rest, and it becomes insensible 
in consequence of its enormous diffusion. 
29. This property of matter and motion is in accord¬ 
ance with the universal law of nature, that not a par¬ 
ticle of matter is ever lost. It is true that it may ap¬ 
pear to suffer annihilation, but its apparent destruction 
is only the commencement of new successions of 
change and of activity. 
Dr. Auckland in bis “ Bridgewater Treatise” beauti¬ 
fully illustrates this principle with reference to that 
invaluable mineral,—coal. He says:— 
“The most early stage to which wo can carry back 
its origin was among the swamps and forests ot the pri¬ 
meval earth, where it nourished in the form of gigantic 
catamites and stately lepidodendra and sigillarirc. 
From their native bed these plants were torn away by 
the storms and inundations of a hot and humid climate, 
and transported into some adjacent lake, estuary, or 
sea. Here they floated on the waters until they sank 
saturated to the bottom, and being buried in the detritus 
of adjacent lands, became transferred to a new estate 
among the members of the mineral kingdom. A lon^ 
interment followed, during which a course of chemical 
chauges and new combinations of their vegetable eje* 
merits have converted them into the mineral condition 
of coal. By the elevating force of subterranean fires,' 
these beds of coal have been uplifted from beneath the 
waters to a new position in the hills and mountains, 
where they arc accessible to the industry of man. 
From this‘fourth stage in its adventures, our coal has 
been n gnin moved by the labours of the miner, assisted 
by the Arts and. Sciences that have co-operated to pro¬ 
duce the Steam Engine and the Safety Lamp. Ke- 
turned once more to the light of day, and a second 
time committed to the waters, it has, by the aid of 
Navigation, been conveyed to the scene of its nest aid 
most considerable changcyby fire, a change during 
which it becomes subservient to the most important 
wants and conveniences of man. Iu this seventh stags 
of its long eventful history, it seems to the vulgar eve 
to undergo annihilation; its elements are indeed re¬ 
leased from the mineral combinations they have main¬ 
tained for.ajres, but their appareut destruction is only 
the commencement of new successions of change and of 
activity. Set free from their long imprisonment, they 
return" to their native atmosphere from, which they 
were absorbed, to take part iri the primeval vegetation 
of the earth. To-morrow thoy may contribute to the 
substance of timber in the trees of our existing forests, 
and having for a while resumed their place in the 
listing vegetable kingdom, may, ere long, be applied a 
second time to the use and benefit of man. And when 
decay or fire shall once more consign them to the earth 
or to the atmosphere, the same elements will enter on 
some further department of their perpetual ministra¬ 
tion in the economy of the material world.”” 
Sydney, March 31st, 1858. F, S. P. 
[To be continued.) 
* Dr. Bucklard’s “Bridgewater Treatise,” p. 481. 
