340 



NATURE 



{Feb. 28, 1878 



sun being magnified to five inches in diameter. Even with the 

 12-inch refractor the occasions suitable for a critical examination 

 are rare. 



In front of the slit I also brought the terminals of the second- 

 ary circuit of an induction coil, which were connected with a 

 Leyden battery. The current through the primary wire of the 

 Ruhmkorfif was furnished by a Gramme machine. This arrange- 

 ment permitted the production of a strong oxygen spectrum near 

 the spectrum of the sun's limb. 



The most obvious point to determine was whether the oxygen 

 lines visible in the spectrum of the solar disc projected beyond 

 the apparent limb of the sun as seen in the spectroscope ; in 

 other words, whether oxygen could be detected in the lower 

 parts of the chromosphere. For this purpose I looked particu- 

 larly at the bases of the prominences. I saw a large number of 

 reversed lines, including some of the more delicate lines of 

 Young's preliminary catalogue, but on no occasion could I be 

 sure that the oxygen lines were seen outside of the limb. Of 

 course, unless such an observation could be made in a perfectly 

 tranquil atmosphere, certainty could not be attained. The ex- 

 periments were terminated temporarily on account of getting my 

 right arm caught in the engine, but they will probably be 

 resumed next summer. 



On examining Prof. Young's catalogue of chromosphere lines 

 made at Sherman Station, in the Rocky Mountains, it appears 

 that he does not note the great oxygen group near G, and as his 

 observations were made with remarkable accuracy and care, this 

 would tend to corroborate the view that the bright-line spectrum 

 of oxygen as seen on the sun's disc must have its upper limit 

 close to the apparent spectroscopic limb of the sun. 



Henry Draper 



Observatory, Hastings-on- Hudson, New York, January 28 



Brain of a Fossil Mammal 



In Nature (vol. xvii. p. 222) is an account of some remark- 

 able characters of the brain of Coryphodon, as determined by 

 Prof. Cope, and recently published in the Proceedings of the 

 American Philosophical Society, vol. xvi. It may interest some 

 of the readers of Nature to know that the subject had been 

 previously investigated by the writer, who published a description 

 and figures of the brain cast of Coryphodon in the American 

 Journal of Science, vol. xi. p. 427, May, 1876, more than a year 

 before the article above quoted appeared. Prof. Cope made no 

 reference to my paper, although perfectly familiar with it. His 

 figures moreover do not represent, even approximately, the brain 

 of Coryphodon, owing to serious errors in his observations, which 

 were based upon an imperfect specimen, as I have shown else- 

 where {American Journal of Science, vol. xiv. p. 83). One of the 

 most glaring of these errors is seen in the supposed olfactory 

 lobes which, as figured, include no small part of the nasal cavities, 

 and naturally add a very remarkable feature to this brain cast. 

 The specimens from which my figures and description were taken 

 are in excellent preservation, and are in the Yale College 

 Museum, where they have been examined by Prof. Huxley and 

 many other anatomists. 



The attention called by Nature to this paper of Prof. Cope's 

 makes the present correction seem necessary for English readers, 

 especially as the paper quoted is a typical one, illustrating the 

 methods and work of its author. O. C. MARSH 



Yale College, New Haven, Conn., February 7 



Origin of Tracheae in Arthropoda 



In Nature (vol. xvii. p. 284) is a notice of a work by Dr. 

 Palmen, of Helsingfors, on the morphology of the tracheal 

 system. From the wording of the notice it appears as if the 

 views of Dr. Palmen as to the origin of tracheae from skin- 

 glands, and as to the importance of Peripatus as an ancestral 

 form of the Tracheata, were new to science. I was, to the best 

 of my belief, the first to discover that Peripatus was provided 

 with tracheal ; and in a paper on the structure and development 

 of Peripatus capensis, published in the Phil. Trans, for 1874, I 

 discussed the question of the origin of tracheae, and put forward 

 exactly similar views to those cited in your notice. These views 

 have been adopted by Prof. Gegenbaur in his new edition of his 

 "Grundriss der Vergleichenden Anatomic " (1878), in so far at 

 least as that Peripatus is placed in a separate division of the 

 Arthropoda, "the Protracheata." Haeckel, following Gegenbaur, 

 supposed his Protracheata to have been provided with tracheal 



gills, but the diffuse arrangement of the tracheae in Peripatus led 

 me to conclude that the ancestral tracheata were terrestrial, and 

 not aquatic, in habit, and that tracheal gills were comparatively 

 late developments. 



I am very glad to find that Dr. Palmen has arrived at similar 

 results. Unfortunately, the place of publication of his treatise 

 is omitted from your notice. It would be of value if you saw 

 fit to append the reference as a note to the present letter. 



Exeter College, Oxford H. N. Moseley 



[Dr. Palmen's paper was published in Helsingfors.— Ed,] 



The " Phantom " Force 1 

 III. 



While very clearly establishing that it is to the force urging a 

 body that the potential energy which the body has not, but can 

 have, must properly be assigned, and calling it very appropriately 

 the "energy of tension," ^ a very apposite remark (which I do not 

 remember to have met with before) is added by "X" in his 

 concluding paragraph?. The body could not command this 

 "force- work" in any position unless it had been put into the 

 proper position to command it ; and the actual energy spent in 

 putting it there is the " energy of tension " which, although for- 

 feited to the force, it can reclaim. In this view it is not sur- 

 prising that potential energy should have the same terms for its 

 measurement as actual energy, since it is nothing but the actual 

 energy which the body, or some agent operating upon it, has 

 really lost; and if we pas from permanent forces to those 

 ephemeral ones which physical agents can produce on an already 

 existing arrangement of bodies, then, according to the existing' 

 configuration of the bodies when the force is generated, and in 

 proportion to the " potential," or to the available statical energy 

 developed, so is the work of the agent used to bestow this energy. 

 In these cases of temporary " potentials " the actions are not 

 actions at a distance, but through an intermediate medium, it may 

 be strung with motion, and with permanent forces, which have 

 absorbed the work applied to put the intervening medium, as 

 it were, on the stretch, and to develop the ephemeral energy of 

 tension. But we recognise this very clearly (as for instance in 

 charging well-insulated electrical conductors) only in the rare 

 cases of reversible arrangements. I'he fatigue and exhaustion 

 which we soon feel when holding out at arm's length a heavy 

 weight (although we do no work upon the weight) arises, for 

 example (like that of a galvanic battery exciting an electro-magnet 

 and supporting a heavy armature), from two causes, the first of 

 which, the excitation of the magnet and armature, and the 

 tightening of the muscles, or producing the requisite statical 

 energy for the occasion, absorb but a small portion of the work. 

 The main expenditure is "frittered away" (a most expressive 

 description of the process, which I owe to Prof. Tait) in aimless 

 and random paths as heat, by the wasteful process of electrical or 

 muscular currents afterwards kept up to maintain the excitation. 



I have thus far sketched out a general view of physics (one 

 which is perfectly adapted to satisfy its general requirements), in 

 which self-balancing actions and reactions, only depending in 

 intensity on the distance between their centres are supposed to 

 be permanently implanted in pairs of material particles, a special 

 case, or fresh assumption regarding the general system of forces 

 contemplated in the Newtonian theory of mechanics, which 

 either may, or may not be the complete theory of their action, 

 but which assists the mind very greatly, by giving them a 

 mechanical explanation, in forming true and correct preliminary 

 notions of the two leading laws of the great modern science of 

 energy. And here I may take the opportunity to mention that my 

 own views of the relationship of modern physics in its various mutu- 

 ally dependent branches to that famous foundation of mechanics 

 which Newton laid (or perhaps I should rather say, since the 

 supremacy of mechanics is by no means yet conceded, of the 

 Newtonian basis of mechanics to modern physics) have been 

 mainly imparted and completed by a perusal of the excellent 

 little manual on "Matter and Motion" by Prof. J. Clerk 



^ Continued from p. 322. 



* The term " statical energy " introduced by Sir W. Thomson (see a note 

 in Prof. Tail's " Sketch of Thermodynamics," p. 52), and now proposed 

 (Nature, vol. xvi. p. 521) by " W. P. O." to be substituted for the above, 

 is of all the phrases yet used to denote it, the truest and simplest description 

 of its real character. That it appertains to the force and not to the body is 

 apparent both from this name and from the definition (which I have endea- 

 voured to illustrate) that it is the "work" of the "agent," a property or 

 possession of that individual, equal and opposite to, but 7iot the same as its 

 ' ' net," or effected work. 



