January 14, 1897] 
NATURE 
247 
Mr. Cumming says that “‘ 2 R 4 = a? is an algebraic equation, 
and as such its symbols express numbers, not things.” Whereas 
I say that truly it is an algebraic equation, and as such its 
symbols may express things and not numbers. A relation 
between numbers is an arithmetical equation, and is appropriate 
to the pure mathematician ; by him algebra was first used, and 
he still clings to the ancient practice ; but physicists have now 
made a perfectly legitimate step onwards and extended the scope 
of the science. Applied mathematics is concerned with things, 
and its symbols may properly be taken to represent concrete 
quantities (see, for instance, NATURE, vol. xxxviii. p. 282). 
Mr. Cumming says that the equation is true in any units ; 
but if he gave his boys R in metres, / in inches, andd in yards, 
or if he used it for finding the curvature of a lens, or the thick- 
ness of a Newton’s-ring film, telling them at the same time that 
the symbols only represent numbers, they might be in a fog. 
A perfectly unnecessary fog, and that is the serious part of the 
business. Artificial difficulties obstruct the path of the beginner 
in regions which are quite easy, and hence it is that his progress 
into higher regions is so slow. Such difficulties need not exist. 
The golfer who keeps on the straight course is untroubled by 
bunkers and obstacles which infest the path of the wild driver. 
If Mr. Cumming can spare time to reconsider the question, 
I know it needs an effort, exferto crede, I am sure it will repay 
him. 
I call the attention of those physicists who are. already 
familiar with the straightforward mode of dealing with concrete 
quantities to the remarkable letter, by Mr. C. S. Jackson of the 
R.M. Academy, Woolwich, immediately preceding Mr. Cum- 
ming’s; and, as he asks me a definite question, IL answers = w/z. 
January 4. OLIVER J. LopGE. 
The Force of a Pound. 
May I suggest to Prof. Perry that it might be well to 
imitate the enemy’s tactics and give a name to the unit of inertia 
on the pound-force system. 
I would propose that, on this system, any piece of matter having 
the .unit quantity of inertia or sluggishness be, for dynamical 
purposes, termed a **slug.” 
The foot-pound (force) -second system might then be equally 
well styled the foot-slug-second system, and under the aspect 
implied by this name would stand on precisely the same footing 
as the centimetre-gram-second, or the foot-pound (mass) -second 
system. 
A “slug” would be an instructive object to contemplate. Its 
virtues would be pretty accurately embodied in a a 32-Ib. shot, 
which, in fact, is manufactured solely for the sake of its inertia, 
and is a body not unfamiliar even to athletic undergraduates in 
our universities. 
I have taught dynamics for many years, both to unprofessional 
students and to engineers, and have remarked that the unit 
difficulty is felt far most strongly by the latter. This I attribute 
in part to the relative inadequacy of the linguistic training which 
many of my engineering students have received before entering 
on their professional studies. They are not well able to dis- 
entangle verbal confusions, and are resentful of them. Conse- 
sequently a liability to trip, arising from some ambiguity of 
terms, which would be a stimulating challenge to a student of 
wider training, is an unmitigated nuisance to the engineer, who 
has no interest in this kind of thing, and does not wish to be 
bothered by it. 
The difficulty is one of language and not of dynamics, and I 
am quite in sympathy with Prof. Perry’s desire to get rid of 
it, and should adopt without hesitation a good text-book which 
employed the pound as the only unit of force, if I knew of such. 
It should always be remembered that, to most students, the 
study of dynamics is the study of the new and unfamiliar pro- 
perty of inertia, and it is only reasonable that the new quantity 
should have a unit witha new and unfamiliar name. 
Torquay, January 4. A. M. WORTHINGTON. 
Sir William MacGregor’s Journey across New Guinea. 
In NATURE of December 17, p. 157, you publish an article 
describing Sir William MacGregor’s interesting journey across 
the South-eastern Peninsula of New Guinea, by Mr. J. Thomson. 
As he has introduced some reference to my work in the Possession, 
perhaps you will kindly allow me space for a few observations. 
The names of seven travellers, besides my own, are mentioned 
NO. 1420, VOL. 55] 
whose attempts ‘*to explore the Alpine region of the Owen 
Stanley Range” have ‘‘ resulted in signal failure.” More than 
one of us, however, d#d@ reach the Alpine regions of the range, 
though none of us ascended Mount Owen Stanley. And I 
cannot think that any of those who made the attempt will feel 
any discredit attaching to them on that account, any more than 
attaches to Sir William MacGregor that he could not reach the 
mountains beyond the sources of the Fly, River.. That Sir 
William was the first to scale Mount Owen Stanley is true, and 
he deserves all the £zdos he has received for his exploit, Yet 
the success which attended his efforts was in no small measure 
due to the information gathered by his forerunners, and even 
by their “signal failures.” Each traveller made it easier for 
his successor ; and Sir William mounted on the backs of all 
who had preceded him, however much the historiographer for 
New Guinea may try to ignore their efforts. The reason why 
some of us who made a not ill-considered effort at great per- 
sonal expense to reach the summit of the Mount, failed in 
accomplishing all we desired, was chiefly one of money. Sir 
William, who has the resources, the steamers and the launches of 
the Possession at his back, and has besides the prestige of 
“Great Chief” over the natives—no mean factor in the ex- 
ploration of such a country—and can call upon his officials in 
all quarters for aid, is in a very different position from a private 
traveller dependent very largely (I speak for myself) on his own 
resources, and owght to accomplish far more than any other 
traveller. 
Mr. Thomson goes on to say: “‘It may be pointed out that 
there seems no doubt that Mr. Forbes did not see the highest 
crest of the mountain from his nearest approach to it, and it is 
almost certain that he could not have obtained access to the 
crown of Mount Victoria [Mount Owen Stanley] along the south- 
eastern spur of it. Concerning this accessible spur, which Mr. 
Forbes proposed ascending, Sir William MacGregor says, it is 
a mighty precipitous buttress, exceeding 12,000 feet in height, 
‘bristling with peaks and pinnacle-like rocks, and contains hun- 
dreds of inaccessible crags and precipices.’” Mr. Thomson’s 
doubts about what I saw or ‘did not see from my nearest approach 
to Mount Owen Stanley; are merely the expression of one 
having no personal knowledge of the country. But if Sir William 
MacGregor—for whose explorations I have the highest admira- 
tion—has said what Mr: Thomson puts into his lips at the close 
of the above extract, it is quite plain that he is not referring to 
the same feature that I have described. I took—and, if I mis- 
take not, have published—a round of bearings upon ‘‘ the highest 
crest,” the most familiar object in my horizon for months. I 
approximately fixed the positions of and placed on my map 
names to these same crags and peaks; but the Lieutenant- 
Governor, following a custom not infrequent with him in regard 
to the geographical nomenclature of his predecessors in this and 
other regions of New Guinea, has renamed them. The “‘ acces- 
sible spur’? mentioned by me, however, was not ‘‘a mighty 
precipitous buttress” — a feature, according to the description, 
one would think, not altogether unrecognisable as such—nor 
yet a Primrose Hill ; but it was a negotiable slope all the same, 
and on a less incline than some others ascended by me in the 
same country. 
In conclusion, I cannot help again drawing the attention 
of cartographers and geographers to the fact that Sir W. 
MacGregor, after all that has been expressed at the Royal 
Geographical Society, and publicly by many writers, on the 
point, still claims for himself the honour of naming the chief 
mountain in the Possession, by persistently calling it Mount 
Victoria, instead of Mount Owen Stanley as it was christened 
nearly half a century ago by Huxley, and has been so inscribed 
on every map all those years. Prof. Huxley himself told me 
that the feature on which he bestowed the name Owen Stanley 
—in honour of as distinguished a commander and explorer as has 
ever sailed in those waters—was not the range, but the mountain, 
whose summit he saw rising clear above the clouds one early 
morning when the A'a¢¢lesmake was lying in Redscar Bay. Its 
position and altitude were then accurately determined. 
Henry O. ForBeEs, 
The Museums, Liverpool, January 4. 
Shooting Stars of January 2, 
Tue shower of shooting stars seen by Dr. H. C. Sorby on the 
morning of January 2, formed evidence of the return of a well- 
known meteor stream which has its radiant in Bode’s modern 
