238 Royal Society. 



ticular year in which this feature attained its limit, and an opposite 

 change commenced, cannot now perhaps be precisely determined ; it 

 was probably somewhat earlier than 18-10. But from the comparison 

 of the magnetic surveys of the British Islands in 1836—37 and 

 1 85 7-jS, it is certain that the change in the direction of the isoclinal 

 lines in this part of the globe has entered upon the contrary phase 

 to that which had previously existed. The observations of the late 

 Mr. Welsh in Scotland in 1857-58 (Brit. Assoc. Reports, 1859), 

 when compared with those of the Scotch Survey made in 1836-37, 

 published in the British xlssociation Reports for 1836, show, according 

 to Mr. Balfour Stewart's calculation, that an increase of several degrees 

 in the angle at which the lines cut the meridians in passing across 

 Scotland has taken place between the epochs of the earlier and the 

 later surveys. The same general conclusion follows from a comparison 

 of the magnetic surveys of England at nearly the same epochs ; every- 

 where near the west coast of England the mean annual secular change 

 in the twenty years has been greater, and near the east coast less than 

 its mean value at Kew ; showing that the general direction of the 

 isoclinal lines more nearly approaches a parallelism to the equator now 

 than it did twenty years ago. The ascertainment of the exact value 

 of the secular change at a particular locality by a well-conducted 

 system of periodical observations is the duty of a magnetic observa- 

 tory ; the direction of the magnetic lines passing across a country 

 is supplied by magnetic surveys ; which, for that purpose, ought to 

 be repeated from time to time, as they have now been in this country, 

 at intervals of perhaps twenty or twenty-five years. 



It has been imagined that the secular changes of the magnetic ele- 

 ments may be due to some alteration taking place either in the dis- 

 tribution or in the condition of the materials in the interior of the 

 globe. But the regularity and uniformity with which the secular 

 magnetic changes continue through long intervals of time, together 

 with their sudden periodic reversals, — and their corresponding fea- 

 tures in the northern and southern hemispheres, which add greatly 

 to the apparent consistency and systematic character of the whole as 

 parts of a uniform general system, — wear more the aspect of effects 

 of some yet unascertained cosmical cause. One of the British Colo- 

 nial Observatories, St. Helena, having the advantage of both a large 

 secular change and a small amount of magnetic disturbance, has 

 afforded a very striking example of the great regularity with which 

 the secular change takes place, maintaining a steady uniformity, 

 traceable not only from year to year, but from month to month, and 

 even from week to week ; so that it is not too much to say that, 

 from observations made during a single fortnight, an annual secular 

 change which has existed almost without variation for more than a 

 century, may be ascertained and measured with very considerable 

 precision. (Magnetic Observations at St. Helena, vol. ii. p. ix.) 



March 2 1 . — " On the Relations of the Vomer, Ethmoid, and In- 

 termaxillary Bones." By John Cleland, M.D. 



" On the Structure and Growth of the Tooth of Echinus." By 

 S. James A. Salter, M.B. Lond., F.L.S., F.G.S. 



