392 



NATURE 



[Feb. 27, 1890 



lead one to suppose that the size Mr. McConnell suggests is 

 ample, not to say generous. I had hitherto supposed that a 

 scientific writer does not necessarily treat of a fresh subject each 

 time he writes. 



Might I add that an index is not a pedigree or diagram, any 

 more than a gazetteer is the same thing as a map ? I fear that 

 to mix up such distinct things would merely introduce an 

 altogether needless difficulty. A Cataloguer. 



The Period of the Long Sea-Waves of Krakatao. 



In connection with the great explosion at KrakatJib at 10 a.m. 

 on August 27, 1883, a great wave was generated, which at 

 Batavia, 100 miles distant, reached a height of 7^ feet above the 

 ordinary sea-level. It was followed by a fairly regular series 

 of fourteen waves, at intervals of about two hours, gradually 

 diminishing in height. Captain Wharton, who writes this part 

 of the Royal Society Report, is much puzzled by the long period. 

 He says : — " If the wave was caused by any sudden displacement 

 of the water, as by the falling of large masses of ejected matter 

 and huge fragments of the missing portion pf Krakatao, or by 

 the violent rush of steam from a submarine vent through the 

 water, it is hardly to be conceived that two hours would elapse 

 before the following wave, the second of the series, started after 

 it. . . . If, however, upheaval of the bottom of the sea, more 

 or less gradual, and lasting fur about an hour, took place, we 

 should have a steady long wave flowing away from the upheaved 

 ai-ea, which as it approached the shore would be piled up con- 

 siderably above its normal height. Thus these waves of long 

 period would be set up. . . . The water would flow back on 

 the motion cea-ing." 



I do not understand how the series of waves would be pro- 

 duced by the sea-bottom being upheaved in the manner described. 

 When the upheaval ceased, the water would probably flow back, 

 and, after the centre of disturbance was reached, a second wave 

 would be generated. But there would be no reason for the 

 water flowing back a second time, and no more waves would be 

 generated. Further, in another part of the Report, we find 

 Prof. Judd expressing the opinion that no upheaval has taken 

 place (p. 25). 



Another explanation has occurred to me, which seems satis- 

 factory. Let us assume, with Prof. Judd, that the first wave 

 was due to a great quantity of fragments falling into the sea. 

 This wave would be reflected by the shores of the Straits several 

 times backwards and forwards, each time giving rise to a fresh 

 disturbance, travelling out towards Batavia through the narrow 

 opening to the east. Opposite Krakatao both on the northern 

 and on the southern shore of the Straits is a great bay. The 

 time a wave would take to travel from Krakatao to the head of 

 the bay on the north is given by Captain Wharton at sixty-one 

 minutes, and the distance to the head of the other bay is much 

 the same. This agrees very well with the two-hour period. 

 Moreover the first disturbance at Batavia would be a rise of 

 ihe water, which was the case. 



In a similar way some of the short periods observed at distant 

 stations may have been due to peculiarities of the channels in 

 which the tide gauges were placed. 



Hotel Buol, Davos. James C. M. McConnel. 



The Distances of the Stars. 



Your note of Prof. Eastman's address to the Philosophical 

 Society of Washington in your columns of February 13 (p. 351) 

 raises some questions of interest on which I think the Professor 

 is mistaken. 



As regards the nearness of particular stars, there are several 

 indications which astronomers have sought to verify by observa- 

 tion and computation. One of these is brightness ; a second is 

 large proper motion, and a third is a bmary system easily 

 separated by the telescope (especially if the period is compara- 

 tively short). Some persons have also supposed that red stars, 

 variable stars, &c., are nearer than most of their neighbours. 

 Stars possessing one or more of these characteristics have been 

 selected for parallax measurements. 



One of these characteristics being brightness, almost every 

 bright star in the northern hemisphere and a good many of those 

 in the southern have been at one time or another measarel for 

 parallax. But no one has attempted to measure the parallax of 

 all stars of the third, fourth, fifth, or sixth magnitudes. Astro- 

 nomers have selected from among these stars those which afford 



some striking indication of nearness, such as the great proper 

 motion of 6l Cygni. If, therefore, we take the parallaxes 

 arrived at in this manner for comparison, we are comparing the 

 results attained for all stars of the first magnitude with those 

 attained for a small number of exceptional stars of the fifth or 

 sixth. 



How far Prof. Eastman's data are otherwise trustworthy I need 

 not consider. I may refer your readers to a very full list of 

 paraxalle> hitheito deteimined, published by Mr. Herbert Sadler 

 in the February number of Knotoledge, by which it will appear 

 how discordant and untrustworthy these results are. But the 

 exceptional character of Prof. Eastman's faint stars is sufficiently 

 evident from the table itsel.f. His first group, with mean magni- 

 tude 5 '57, has a mean proper m< tion of 4" '93 ; the second group, 

 with a mean magnitude 5 '59, has a mean proper motion 2"'33. 

 Surely Prof. Eastman does not mean that the average pi'oper 

 motion of stars of the magnitude 5 "58 is 3" '63. There is not 

 one star in a hundred of this degree of faintness which possesses 

 such a proper motion as this. W. H. S. MoNCK. 



Dublin, February 15. 



P. S. — It is possible that a sphere enclosing the thirty nearest 

 stars to us would include more faint stars than bright ones ; but 

 I think it certain that it would not include as large a percentage 

 of fifth magnitude stars as of first magnitude stars. The first 

 magnitude stars do not exceed twenty, and a fe\y of them seem 

 to be very distant. The fifth magnitude stars are reckoned by 

 hundreds, and a few of them are comparatively near. 



The Longevity of Textural Elements, particularly 

 in Dentine and Bone. 



Whatever views we may take of the theories of Weismann, 

 which at present occupy the attention of biologists, they may be 

 hailed as giving new directions to research, and one of the sub- 

 jects about which his allusions will probably lead to further 

 inquiry is the length of time durin'^ which textural elements con- 

 tinue individually. I have used the word longevity at the top of 

 this letter ; but, perfectly admitting the justice of Weistnann's 

 criticism — that division into two, each of which is a unity like the 

 first, is not death — I feel driven to the dire necessity of invent- 

 ing a new word, permanunity, to denote permanence without 

 division ; and it is of such permanence or longevity of the un- 

 divided unit that I wish to note a circumstance which has 

 recently presented itself to my mind. 



Every anatomist is aware that the living elements of dentine 

 are nucleated corpuscles with elongated branches, which are 

 embedded in the matrix, and lengthen as the dentine increases 

 in thickness, while the corpuscles themselves retire inwards, re- 

 maining at the boundary of the lessening pulp-cavity. The con- 

 tinuity of the tubes containing these finres furnishes, as soon as 

 one thinks of it, convincing proof that they are the same 

 branches and the same dentine corpuscles which are found when 

 the dentine begins to be deposited and when it is completed. 

 But the dentine begins in childhood, and may go on increasing 

 in thickness in old age, with its tubes still continuous, though 

 losing their retjularity of position. Therefore, dentine-corpuscles 

 continue alive and without division through the greater part of 

 the life of the organism. 



The interest of this is exceedingly great, if the relation of 

 dentine to bone be considered. Bone has a matrix similar to 

 dentine, and has branched corpuscles ; but the bone-corpuscles 

 ditfer from the dentine-corpuscles in becoming completely em- 

 bedded in the mineralized matrix, without any attempt to retire 

 from it, and thus come to have branches on every side. Under 

 the microscope one can see in compact bony tissue that there is 

 a continual reabsorption and redeposition of bone going on ; and 

 these alternating processes are brought about in a way which is 

 easy to understand, though very generally misapprehended. In 

 consequence, probably, of the very pressure exercised by the 

 bony deposit on the corpuscles, the corpuscles are excited to 

 absorb it ; and one sees absorption spaces commencing sometimes 

 in the centres of haversian systems, and sometimes in individual 

 lacunae. The activity thus aroused in the corpuscles causes them 

 to enlarge and to attempt proliferation ; which being in the first 

 instance modified by their close surroundings leads to their being 

 converted into large multinucleated masses, the so-called giant- 

 cells or osteoclasts. But when a greater amount of room has 

 been obtained, these masses separate up into corpuscles with ore 

 nucleus each, bone-corpuscles or osteoblasts, which, arrayirg 

 themselves around the cavity, initiate the formation of new 



