July I, 1875] 



NATURE 



163 



to address such an audience, either with the pen or the 

 voice, and gave as an illustration a great meeting con- 

 vened by his fellow-citizens to welcome him back to 

 Canada after he had been knighted. He was, of course, 

 expected to say something of himself and of his visit to 

 Europe. He tried his best, he said, but soon grasping a 

 long pointer, turned round to some maps and diagrams 

 illustrative of the geology of Canada, and only recovered 

 his peace of mind and command of language when he 

 found himself once more among Laurentian, Huronian, 

 gneiss, limestone, and the rest of his beloved rocks. 

 Nevertheless, he kept copious journals of his various 

 expeditions, and illustrated them with most admirable 

 pen-and-ink sketches. A selection from these could 

 hardly fail to be of great interest, both in relation to the 

 man himself and to the way in which geology has to be 

 carried on amid the wild life of the backwoods. 



By those who were privileged with his friendship. Sir 

 William Logan will be affectionately remembered as a 

 frank, earnest, simple-hearted man, ever gentle and help- 

 ful, enthusiastically devoted to his profession, and never 

 happier than when discussing geological questions in a 

 Ute-d-tcte, full of quiet humour, too, and showing by 

 many a playful sally in the midst of his more serious talk, 

 the geniality and brightness of his sunny nature. Peace 

 to his memory ! He has done a great work in his time, 

 and has left a name and an example to be cherished 

 among the honoured possessions of geology. 



Arch. Geikie 



TREVANDRUM MAGNETIC OBSERVATIONS 

 Observations of Magnetic Declination made at Trevan- 

 druin and Agustia Malley in the Obsei vatories of his 

 Highness the Maharajah of Trava?icore, G.C.S.I, in 

 the Years 1852 to 1869. Vol. i. Discussed and edited 

 by John Allan Broun, F.R.S., late Director of the 

 Observatories. (London : Henry S. King and Co.) 



WE have heard a great deal lately about the native 

 rulers of India, and the worst features of one of 

 them have been brought very prominently before us ; but 

 it|is a pleasing reflection that they are not all like the poten- 

 tate of Baroda, while some of them might even read a 

 lesson to the paramount power. Let us hear what Mr. J. 

 Allan Broun, a magnetician of great eminence, has to say 

 of the late ruler of Travancore. 



" The Trevandrum Observatory," he tells us, " owed its 

 origin in 1836 to the enlightened views of his Highness 

 Rama Vurmah, the reigning Rajah of Travancore, and to 

 the encouragement given to them by the late General 

 Stuart P'raser, then representing the British Government 

 at Trevandrum. His Highness, desirous that his country 

 should partake with European nations in scientific inves- 

 tigations, sanctioned the construction of an observatory, 

 named Mr. Caldecott its director, and gave him power to 

 furnish it with the best instruments to be obtained in 

 Europe." 



The peculiar position of Trevandrum, not far from the 

 magnetic equator, induced Mr. Caldecott, with the Rajah's 

 permission, to procure from Europe a complete equipment 

 of the best instruments for magnetic and meteorological 

 observations, and to build a magnetic observatory, which 

 was completed in 1841. 



Mr, Caldecott died at Trevandrum in 1849, and the 



observatory was in January 1852 placed under the direc- 

 tion of Mr. John Allan Broun, who had previously directed 

 with well-known success the observatory of Sir T. Bris- 

 bane at Makerstoun, in Scotland. 



Mr. Broun began his office with the conception of an 

 interesting and important problem in terrestrial magne- 

 tism, which he was determined as far as possible to work 

 out. This would render it necessary that the observations 

 should not be limited to a single station. He wished, 

 among other things, to determine how far the physical 

 constants of terrestrial magnetism and their various 

 changes depend on differences of height, of latitude, and 

 of longitude. 



The Agustia Malley, the highest mountain in the neigh- 

 bourhood, was chosen as affording the best means for 

 determining the effect of height, and accordingly Mr. 

 Broun resolved to erect an affiliated observatory on this 

 nearly inaccessible rocky peak, surrounded by forests, the 

 inhabitants of which were elephants and tigers. These 

 and all other difficulties connected with this formidable 

 undertaking were, however, completely vanquished, and 

 the Agustia Observatory was completed in 1855. 



We learn from Mr. Broun that his labours were not 

 entirely confined to these two observatories. "Other 

 observations," he tells us, especially of magnetic declina- 

 tion, were made simultaneously " during short periods at 

 different stations in Travancore, as nearly as possible on 

 the magnetic equator, 90 miles north of Trevandrum, and 

 also 40 miles to the south. Observations connected with 

 meteorological questions were also made simultaneously 

 to the east and west, and about 5,000 feet below the 

 Agustia peak, on the peak itself, and at Trevandrum ; 

 while on one occasion hourly observations were made 

 during a month at five different stations, varying gradually 

 in height from the Trevandrum Observatory (200 feet) to 

 6,200 feet above the] sea-level, in which fifteen observers 

 were employed." 



In this first volume Mr. Broun has confined himself to 

 the magnetic declination, and one of the chief objects 

 sought has been to determine every possible action of the 

 sun and moon upon the magnetic needle. The observa- 

 tions extend from 1852 to 1870, and embrace in all nearly 

 three hundred and forty thousand readings. 



A considerable portion of the introduction is devoted 

 to the discussion of a question which has, we think, been 

 somewhat too much overlooked. When a magnet is 

 suspended by a thread and enclosed in an appropriate 

 box, it does not necessarily follow that all its movements 

 are due to magnetic causes, for changes in temperature and 

 humidity may affect the zero of torsion of the thread, and 

 thus cause slight changes in the position of the suspended 

 magnet. It is perhaps unlikely that such changes could 

 seriously affect the character of the daily variation, but it 

 has been [thought that they might perceptibly affect the 

 annual variation, since in this case the magnetic change 

 is comparatively small, while the range of temperature 

 and humidity is generally great. 



Mr. Broun overcame this source of error by obser- 

 vations of an unmagnetic brass bar suspended in the 

 same way as the magnet, which thus afforded him the 

 means of estimating, and hence eliminating, the error 

 due to these causes. ^ 



Besides all this, several declinometers were used and 



