346 



NATURE 



\Feb. 13, 1890 



These strong protests had the desired effect for the time 

 being, and it was not till 1853 that another attempt was 

 made to bring a railway within the Park. This was by 

 the South-Eastern Company, and being postponed for a 

 year, was not heard of again. In 1863, however, the 

 London, Chatham, and Dover Company proposed a line 

 from Dulwich to Epsom passing within 700 feet of the 

 Observatory ; and the South London, Greenwich, and 

 Woolwich Railway another passing within 600 feet. Sir 

 George Airy was at first inclined to think that, if these 

 railways were laid in tunnels, they might be permitted. 

 But as facilities for mak ng experiments had meantime 

 increased with the multiplicity of lines, he renewed his 

 investigations at the suggestion of the Hydrographer, 

 and found that the protection of the tunnel was by no 

 means established ; and in other respects he had been if 

 anything too lenient in assigning minimum distances. 

 His conclusions from the experiments were : — 



" L It is indispensable that the railway pass through 

 the Park in a covered tunnel. 



" II. It is indispensable that its minimum distance from 

 the transit circle of the Royal Observatory exceed 1000 

 feet." 



The result of all these independent experiments seem 

 to be that even with small instruments, such as a sextant 

 or a small telescope, vibration is sensible at 1000 feet 

 distance ; and that though a tunnel may be a protection 

 in some cases (we shall presently find reason to question 

 this more seriously) the reasons are not sufficiently under- 

 stood to enable us to predict the influence of individual 

 tunnels. All the observations, except one of Dr. Robin- 

 son's, have reference to reflection observations ; but it 

 does not follow that these are the only observations dis- 

 turbed, as is made abundantly clear by the single observa- 

 tion of Dr. Robinson's referred to, where the telescope 

 was practically shaken to another position against the 

 clamp. It is in reflection observations that the vibration 

 is most easily discernible, but errors introduced into other 

 observations are no less serious because they are not 

 readily detected. Observation with mercury is a delicate 

 test, but it is quite possible that we may very soon find 

 even a more delicate test necessary. We are, for instance, 

 only on the threshold of photographic experiments for 

 which the most perfect steadiness is essential ; and it is 

 of the utmost importance to make sure that our large 

 Observatories are so protected as to be available for such 

 work as is gathering shape in the mists of the near future. 

 If any mistake has been made in dealing with railway 

 proposals, it has been that of being too lenient ; firstly, 

 from the desire to yield as far as possible in matters 

 affecting public convenience ; and, secondly, perhaps 

 from not fully appreciating the remark of Captain 

 Beaufort in 1835, that the results obtained with small 

 instruments must be properly magnified for deahng with 

 large ones. This point has been made clear by the last 

 case we shall quote, also from the history of the Royal 

 Observatory. Proposals for an adjacent railway were 

 renewed, as we have said above, in 1888. It had been 

 already noticed that the lines which had been permitted 

 were not sufficiently remote to prevent disturbance, and 

 accordingly experiments were now made with the transit 

 circle itselt instead of with a small instrument. An observer 

 was stationed at the transit circle prepared for a nadir 

 observation, and for an hour noted the times when the 

 images were steady, when partially disturbed, and when 

 so agitated as to prevent observation. These times were 

 noted carefully by a standard clock to within a few seconds. 

 Other observers were furnished with watches set to 

 standard time, and travelling on the various lines of 

 railway in the neighbouthood noted the exact times of 

 stopping and starting of all trains, entries into tunnels, &c. 

 The observations were made near midnight when other 

 traffic was stopped. On the following day the indepen- 

 dent records of the transit circle observer and the train 



observers were compared. These operations were re- 

 peated on five separate nights. The result of the series 

 of observations may be gathered from the following 

 extract from the Report of the Astronomer-Royal to the 

 Board of Visitors, 1888 June 2 : — 



" It resulted from these experiments that trains on the 

 Greenwich-Maze Hill Railway caused great disturbance 

 during their passage, not only on the section between 

 Greenwich and Maze Hill, the nearest point of which is 

 570 yards from the transit circle, but also on the line 

 beyond Greenwich on the London side, and beyond Maze 

 Hill on the Woolwich side. The distances of the Green- 

 wich and Maze Hill Stations from the Observatory are 

 about 970 and 670 yards respectively . . . The disturbance 

 was very great during the passage between Greenwich 

 and Maze Hill, the reflected image being invisible while 

 the train was in the tunnel, at a minimum distance of 570 

 yards, and there was considerable disturbance during the 

 passage of trains through the Blackheath-Charlton tunnel, 

 at a distance of a mile, the reflected image becoming 

 occasionally invisible." 



It thus appears that the tunnels increased rather than 

 diminished the disturbance ; and that the minimum dis- 

 tance for insensible tremor had been considerably under- 

 estimated. But the interference with the work of the 

 Observatory is not serious. By the vigorous action of 

 Sir George Airy and his successor the national Observa- 

 tory has been saved from the misfortunes which have 

 befallen Paris and Berlin, where traffic has been allowed 

 to make certain classes of observation impossible. 



H. H. Turner. 



TITANOTHERIUM IN THE BRITISH 

 MUSEUM. 



T^O those English zoologists who have not had the 

 ■*■ good fortune to visit the palaeontological museums 

 of the United States the huge Miocene mammals form- 

 ing the family Titanotheriidce have been hitherto known 

 only by description and small-sized figures of the skull 

 and skeleton, which, however excellent they may be, afford 

 but a very inadequate idea of the proportions of these most 

 remarkable Perissodactyle Ungulates. Recently, how- 

 ever. Prof. O. C. Marsh, of New Haven, to whose 

 generosity our National Museum is already much indebted, 

 has presented that institution with a beautifully executed 

 model of the skull of one of these mighty brutes, v/hich 

 is now exhibited in the front palaeontological gallery, below 

 the head of the skeleton of the Kentucky mastodon. By 

 singular good fortune the Keeper of the Geological 

 Department of the Museum has been enabled at the 

 same time to purchase associate d examples of the teeth 

 of another member of the family, which are placed along- 

 side of the cast, and thus enable us to see the actual state 

 of preservation in which the remains of these creatures 

 are found. 



The TitanotheriidcB were first made known to science 

 from the evidence of specimens of the dentition described 

 years ago by the French naturalist Pomel, by whom the 

 name Menodus was proposed for their owner. Unluckily, 

 however, this name was preoccupied by the earlier 

 Menodon; and we are therefore compelled to adopt for 

 the type member of the family the name Titanotheriuvi, 

 which is the first of the numerous terms proposed by 

 American writers. The species of which the skull has 

 been presented to the Museum is made by Prof. Marsh 

 the type of a distinct genus under the name of Brontops. 

 The chief distinction of this form from the type of 

 Brontotherhtm, which seems inseparable from Titano: 

 iherium, appears to be the reduced number of incisors, 

 but if writers like the Director of the Museum are right 

 in regarding such variations in the allied group of the 



