202 



NATURE 



{Jan. 11,1872 



which the body is moving. If difference of specific gravity be 

 regarded as the impelling cause of any current, the deflecting 

 power of rotation will certainly be infinitesimah 



Difference of specific gravity, resulting from difference of tem- 

 perature between the ocean in equatorial and polar regions, 

 might, if sufficiently great, produce some such interchange of 

 equatorial and polar water as Dr. Carpenter supposes ; but 

 surely the difference of temperature between the equator and 

 the poles could not produce currents like the equatorial cur- 

 rent and Gulf Stream in a wide expanse of water. Such a 

 general difference of temperature might tend to produce a 

 general motion of the ocean ; but it is inconceivable that it 

 should produce motion in particular parts of the ocean, as 

 Maury, Colding, and others, conclude. 



But I think it is by no means difficult to prove that the cir- 

 culation of the waters of the ocean cannot be due to the 

 difference of temperature between the equatorial and polar 

 regions. And Dr. Carpenter must be mistaken in supposing 

 that it requires great mathematical sliiU to determine the value oi 

 the forces to which he attributes the circulation of the ocean. The 

 whole subject, when properly vieM-ed, resolves itself into a me- 

 chanical problem of such e.xtreme simplicity as not to require for 

 its solution the aid of any mathematics whatever in the ordinary 

 sense of the term. Taking Dr. Carpenter's own data as to the 

 difference of temperature between the waters at the equator and 

 the poles, and al.so his estimate of the rate at which the tempera- 

 ture of the equatorial waters decreases from the surface down- 

 wards, I have, in my paper in the P/iilosophkal Magazine for 

 October last, proved that the amount of force which gravity 

 exerts on, say, a pound of water, tending to make it move from 

 the equator to the poles supposing the pound of water to be 

 placed under the most favourable circumstances possible, is 

 only -5^5 of a grain. 



I have shown also that the greatest amount of imrh that 

 gravity can perform in impelling the waters from the equator 

 to the poles as a surface current, and back from the poles 

 to the equator as an under current (assuming that the waters 

 would actually move under an impulse so infinitesimal) is 

 only nine foot-pounds per pound of water. And in regard 

 to the Gibraltar current, the amount of work which gravity 

 can perform does not exceed one foot-pound per pound. 



If these results be anything like correct, and it be ad- 

 mitted that a force so small is insufficient to produce the ne- 

 cessary motion, then it is needless to expect that any future 

 observations in reference to currents of the ocean will in the least 

 degree aid Dr. Carpenter's theory ; for, supposing it were found 

 that the waters of the ocean do circulate in some such manner 

 as he concludes — a supposition very improbable — still we should 

 be obliged to refer the motion of the water to some other cause 

 than to that of differences of temperature. James Croll 



Edinburgh, Dec. 22, 187 1 



"Nature Worship" 



In a spirited article under this title in the last number of the 

 Meilieal Times and Gazette, we are accused of "the most dismal 

 want of appreciation of the true scope of the medical art and 

 science." This is hard ! The ground for it is to be found in 

 the following sentences in the short notice of the Brown Institu- 

 tion in Nature of Dec. 21 : — ■ 



" The true physician fears to meddle with the processes of 

 which he is the attentive and anxious spectator. Although the 

 more ignorant members of the medical craft — the so-called 

 * practical' men — may sometimes, with the best intentions, ex- 

 periment on their patients with harmful drugs, such experimen- 

 tation i. repudiated by the man of Science." 



If objecdon had been taken by our guarded suggestion that it 

 may happen that practitioners may sometimes use powerful agents 

 by way of remedies without any adequate knowledge of their 

 properly, we should not have been surprised, and would have 

 been very willing to apologise had we been assured that the in- 

 sinuation was unfounded. What our critic finds fault with, how- 

 ever, is the second part of the sentence, viz., our assertion 

 that such experimentation on human beings with harmful drugs 

 is olijec'ionable. If experiments had never been made on human 

 beings, he argues, we should not have learnt to know some of 

 our most useful and valuable drugs. This may be so ; but even 

 if it is, it perhaps scarcely affords a sufficient justification for a 

 continuance of the practice. 



In another part of the article we are accused of "uncon- 

 sciously reproducing the superstitious and false philosophy of 



2,000 years back," and we are distinguished by the epithet 

 " Nature worshippers." Let us quote the superstitious sentence 

 which has laid us open to so unexpected an imputation: 



" The pathologist at the bed.side is not in the position of an 

 experimenter, but only in that of a student, who stands by at a 

 greater or less distance ; while another over which he has no 

 control performs experiments in his presence without deigning to 

 explain to him their nature or purpose." 



By these words we are supposed to imply that while nature 

 works we worship. Does the student who stands by while the 

 professor performs an experiment in his presence, the nature of 

 which he very imperfectly understands, ready to help if need be, 

 but fearing to meddle or even ask a question least he spoil the 

 wished-for result, worship his teacher ? Or is it the mere speaking 

 of Nature as a teacher at all that is superstitious and unphiloso- 

 phical ? 



The truth is, that our contemporary has obviously found the 

 sentences quoted from our article a convenient text for a telling 

 homily on a subject with which our remarks had nothnig what- 

 ever to do. Our object was to point out that for the purposes of 

 pathological invesdgation, and for trying the action of unknown 

 remedies, a fellow mortal stretched on a sick bed is not a fit sub- 

 ject ; that it is better to use dogs, cats, ami rabbits. His aim, 

 on the other hand, is to impress upon his readers the important 

 practical lesson, that the doctor when called to see a patient 

 must not stand by inactive, but use every means at his disposal 

 for the relief of suffering and the prolongation of life. If he had 

 found that he could add force to the admonition by clothing it in 

 figurative language, and had said that the physician should 

 grapple with the disease as with a fiend, it would not have 

 occurred to us to call him a "devil worshipper." 



The Writer of the Notice 



Prof. Helmholtz and Prof. Jevons 



Jealous of any and every restriction to that full liberty of 

 scientific thought which cannot be over-advocated, we have re- 

 cently gone so far as to deny the necessary and universal validity 

 of the old axioms or "self-evident principles," not only in 

 geometry, but in logic. Now I would submit that, if without 

 some elementary or initial certainties all scientific thought is im- 

 possible, we must either retract these denials altogether, or so far 

 limit them as to leave the logical certainties intact. But can we 

 do the latler while geometrical axioms are in dispute ? Towards 

 answering this question, I propose to consider the hypothesis ad- 

 vanced by Prof. Helmholtz, to be found in Nature, No. 103, 

 October 19, and ably commented on by Prof. Jevons. 



In order to show how geometrical axioms, with conclusions 

 based thereon, may not be necessarily or universally true, Prof. 

 Helmholtz tells us " to imagine the existence of creatures whose 

 bodies should have no thickness, and who should live in the mere 

 superficies of an empty globe," and then, as a consequence, to 

 admit that, "while, with us, the three angles of a rectilineal 

 triangle are exactly equal to two right angles, with them, the 

 angles of a triangle would always, more or less, exceed two 

 right angles." I propose to show that this position, so far as it 

 affects the question, contains a logical uncertainty and unsound- 

 ness, which, if admitted, would vitiate all reasonings whatsoever. 



We should premise that the "imagined creatures" are sup- 

 posed to be "in possession of human powers of intellect," 

 however their external conditions differ from ours. This assumed 

 (and conceded). Prof. Helmholtz has to prove that the assumed 

 difference of the external conditions will necessitate the in- 

 tellectual difference assigned in his hypothesis ; but he cannot 

 assume this also without begging the whole question. 



Let us first a'ik, what here is the import of the expression, 

 "with them, the angles of a triangle would always, more or 

 less, exceed iwo right angles"? To take the term "e.xceed," 

 do the supposed beings detect the excess, or not ? If they do, 

 they find these three angles exceed two of our right angles, and 

 they are acquainted with our right angles, and are consequently 

 capable of conceiving four such rectilinear angles, and, thence, 

 a rectilinear triangle with all its angles together equal to two 

 right angles ; and thus the entire supposition is unproductive. 

 If we assert now that they do not detect the excess because they 

 cannot, under their new conditions, conceive a rectilinear figure, 

 we are simply begt;ingthe question we proposed to institute, viz., 

 whether we derive our geometrical notions through our con- 

 ditions, or whether these notions are intuitive ? And, lastly, if 

 we say that the beings in question take the spherical angles they 

 have for rectilinear angles, and their four equal angles about a 



