Januaky, 1903.] 



KNOWLEDGE. 



narrow aud ill-develoi)ed. Some of these poor specimens, 

 if exammed as they approach, as to their pectoral pedometer 

 alone, would be taken for mules, which resemble them most 

 c'losely in this particular, and indeed in general build as 

 well. It is not necessary to do more than point out the 

 close correspondence of the relative locomotive activities 

 of the horse, ass, and mule with the degree of development 

 of the pectoral, as was seen in the case of the inguinal 

 pedometer. 



In point of importance, from the preseat aspect of them, 

 the pedometers in the inguinal, pectoral, and post-humeral 

 regions may be numbered 1, 2, 3. 



There are several other situations of the animal body 

 where whorls, featherings, aud crests occur, but these three 

 that have been mentioned are the only ones that can be 

 described as pedometers, the others being either due to 

 pressure or being secondary to general muscular activity, 

 as in the sides oif the neck, but not being by-products of 

 locomotive activity per se. The horse, again, is pre-eminent 

 in these other whorls, inasmuch as it presents no fewer 

 than three invariably, and nine frequently. 



A few facts concerning these particular whorls, feather- 

 ings, and crests may be alluded to in conclusion : — 



1. — They occur in a direct ratio with general muscular 

 development in an animal, and the difference between the 

 size and definition of the whorl of an animal which is 

 large and fat, but not muscuhir in proportion, and an 

 animal which shows good muscular development, is very 

 significant. 



2. — They never occur over the middle of one large 

 muscle, and only where groups of muscles underlying the 

 part exercise traction in opposing directions. 



3. — They never occur in Carnivores ; though here it may 

 be said exceptio prohat regidam, for two out of the vast 

 number of Carnivores examined, viz., two long-bodied 

 domestic dogs of the dachshund type, with very strong 

 fore-quarters, showed a rudimentary post-humeral whorl. 



It may prevent misconception to state here that the 

 tenu " pedometer " is used loosely, and chiefly by way of 

 illustration, but that it is faithful to the facts, which are 

 of a simple order, and open to the study of all whom they 

 may concern. 



THE SUN'S DUSKY VEIL. 



By Miss Agnes M. Clekke. 



None of the solar appurtenances is more obvious to 

 inspection than the screen of attenuated matter over- 

 spreading the photosphere. Already, in 1G12, Lucas 

 Valerius recognised the darkening of the sun's limb which 

 results from its action. Bouguer, more than a century 

 later, measured the gradations of darkening ; Laplace 

 calculated, from the basis of Bouguer's measures, the total 

 amount of light-stoppage in the so-called atmosphere ; and 

 Father Secchi jjerceived the stoppage to be selective, the 

 surviving marginal rays showing a rufous hue. Moreover, 

 since those are very imperfectly actinic, photographs of 

 the sun exhibit the edges of the disc as much more obscure 

 than they appear to the eye. The solar and terrestrial 

 atmospheres are thou so far alike that both are heavily 

 absorptive of blue light, while transmitting red aud yellow 

 beams with comparative freedom. Yet it does not follow 

 that the sun rcseiubles (he earth iu being surrounded by 

 an envelope nf refrigerated gases. This is indeed impos- 

 sible under the given conditions. Let us briefly recall 

 their nature. 



The Sim's tinted screen must be situate I in the imme- 



diate neighbourhood of the photosphere.* Paculae visibly 

 overtop it ; their upper sections escajje the dimming effects 

 of its intervention. They seem like half-submerged stakes 

 in a tideway, that serve, not only to mark the channel, but 

 to show the depth of the water. Now facul» themselves 

 can be readily located. They are clearly photospheric 

 protuberances. This relationship attests itself indeed 

 to the eye, yet still more convincingly by spectroscopic 

 evidence. Facular light is impressed with the whole array 

 of Fraunhofer lines. It escapes none of the absorption 

 exercised by the vaporous layers near the sun. It has 

 then demonstrably been sifted through them. Facute, 

 then, i-ise from the photosphere, sunnount the screening 

 envelope, and are immersed iu the reversing stratum. A 

 vaporous layer, however, lying between the reversing 

 stratum and the photosphere, should necessarily be incan- 

 descent ; and incandescent gases stop only special luminous 

 vibrations ; they are incapable of producing a general 

 absorption, such as shadows the solar limb. Hence the 

 interpc^sing veil can only be of a pulverulent composition ; 

 cool vapours, placed in the torrid situation where it exists, 

 should, in a few minutes, become glowing ; and the action 

 of glowing vapours would be indistinguishable from that 

 of the reversing layers. 



But whatever its constitution, there can be no doubt as 

 to the importance of its function in the solar economy. 

 Stripped of its " atmosphere," the sun would appear fully 

 one stellar magnitude brighter than it actually does. The 

 change might be described as equivalent to the rise of 

 Aldebaran to the rank of Arcturus. Further, its thermal 

 power would be nearly doubled.f As one result of the 

 subsisting arrangement, then, the solar expenditure of 

 energy is strongly controlled. The resources of the great 

 globe are husbanded, aud its vital span must be propor- 

 tionately lengthened. Hence the solar stage of development 

 may be inferred, on this ground alone, to be one of relative 

 permanence. I'or white stars, radiating from bare photo- 

 spheres, waste their stock of power recklessly ; while the 

 provision of a " niggard " apparatus iu later life prolongs 

 existence by economising the means of sustenance. 



Dr. J. Halm is perhaps the first investigator adequately 

 to appreciate the significance of that darkening of the sun's 

 limb which is so easy to observe, so difiicult to account 

 for. " One would have thought," he writeslj;, " that such 

 an important fact as this (juite enormous light-and-heat- 

 absorbing faculty of the solar atmosphere would have led 

 solar physicists to enquire whether, in view of the 

 stu]K'ndous changes going on incessantly at the siin's 

 surface, wc can possibly rely on the absolute constancy of 

 the solar envelojie, or whether the density of the absorbing 

 matter might not rather be exposed to variations which 

 would lead to serious consequences as regards the main- 

 tenance of the thermal equilibrium iu the solar body. So 

 far as we know, however, such an attempt has never l>eea 

 made." 



But the author has evidently overlooked the enquiry 

 jstarted in 1890 by Mr. Wilson, of Daramoua, aud Dr. 

 Kambaut. the [iresent Radclift'e observer, as to the real 

 occurrence of just the variations in question. § They 

 laid down the plan of observations designed to extend 



* Ur. Scheiiur, it is true, places it in the chromosphere (" Strahlimg 

 and Tem(^ioi!itiir dor Sonne," p. 50), but gives uo satist'aetor/ reason 

 lor the trHiisforonce. 



t Professor Frost found, from an elaborate series of eiperimeuts, 

 that llie sun's output of heat would be augmented t'7 times by the 

 removal of its absorbing envelope (Astronomy and Astrophysics, 

 Vol. XL, p. 731). 



X Annals oj the Royal ObsernatO'-y, Edinburgh, Vol. I., p. 7i. 



§ Pruc. Roiial Irxsli Academu, May 9th, 1892. 



