April 30, 1896] 



NATURE 



619 



Let this movable matter be kept in a state of steady motion 

 relative to the sphere, by actions and reactions between it and 

 the sphere, without the action of any external force : 



Let P be the pole of the axis of rotation of the sphere, which 

 will also be its momental axis : 



Let Q be the momental axis of the total motions of the 

 movable matter relative to the sphere : 



Let I be the moment of inertia of the sphere, and M the 

 total moment of momentum of all the movable matter around 

 the axis Q : • 



Then shall the sphere take such a motion that the pole P, 

 while remaining in a fixed direction in space from the centre of 

 the sphere, shall move steadily relatively to the matter of the 

 sphere around the pole Q, with an angular velocity M/L 



The application of this theorem to the case of the earth 

 surrounded by its oceanic and atmospheric envelopes can now 

 readily be seen. To obtain the value of M, we may roughly 

 estimate the ratio of the moment of inertia of the earth to 

 that of the ocean as 2600, and to that of the atmosphere as 

 1,000,000. 



Ol)seryations, as discussed by Chandler, and interpreted by 

 theory, indicate an annual change in the pole of the earth, 

 which would be produced by a primary oscillation back and 

 forth through a length of ten feet, or a revolution in a circle 

 having a diameter of five feet. The former motion would, 

 according to the theorem, be the necessary result of a general 

 motion of the oceans on the two sides of the earth, which, at 

 the point where the motion was a maximum, would be 2600 

 times as great. Approximately this motion would be represented 

 by a continuous flow of the central parts of the Pacific ocean 

 toward the pole of about 150 feet per day, with a correspond- 

 ingly larger motion of the Atlantic in the opposite direction ; 

 followed by an opposite oscillation during the other six months. 

 If, as may seem very likely, there cannot be so great a differ- 

 ential flow as this through Behring Strait, and between the 

 American and Asiatic continents, it will be necessary to suppose 

 a more rapid flow elsewhere, or a sufticient vortex in the 

 currents of the Atlantic and Pacific oceans. Whether the 

 currents in these oceans are deep enough to produce the observed 

 effect must be left to hydrographers to decide. 



Passing to the atmosphere, the excess of motion through one 

 season over that of the other season, to and from the north 

 direction, amounting to 4000 miles in six months, or say twenty 

 miles per day, would also account for the observed change. In 

 these statements respecting the required motions of the earth 

 and atmosphere, I have presupposed a motion around an in- 

 variable momental axis. If the motions are such that their 

 momental axis moves around the earth in the course of a year, 

 the required differential motions between the opposite seasons 

 would be only half as great. 



In what precedes I have spoken of the earth as a sphere, and 

 considered only differential motions. The actual earth being a 

 spheroid, the motion of the pole already described would not 

 be continuous. The actual effect of oceanic and atmospheric 

 currents of a permanent character on the terrestrial spheroid 

 would be to displace the mean pole of the earth from its pole of 

 figure to such a point of equilibrium that the motion described 

 in the theorem would be neutralised by an equal and opposite 

 luiierian motion, due to the ellipticity of the spheroid. The 

 actual effect would be a revolution of the terrestrial pole, ac- 

 cording to the known laws of rotation, around the central point 

 of equilibrium thus fixed in 427 days. Just what the displace- 

 ment is can be only a matter of guess-work ; from the known 

 magnitude of the ocean currents they might produce a displace- 

 ment ranging from ten to twenty feet. 



A brief statement of the character of the theoretical variations 

 of the latitude, due to these causes, may not be inappropriate. 

 Since the directions of the currents of the air and ocean go 

 ihrcjugh an annual period, we should expect a corresponding 

 peritMj in the latitude. Since, however, the amount of the 

 annual change varies irregularly from year to year, though 

 remaining constant in the general mean, the amplitude of the 

 annual term should be subject to small variations from time 

 to time, while preserving its mean value unchanged from age 

 to aije. 



On the other hand, the amplitude of the Eulerian motion 



being permanently increased or diminished by every meteoro- 



- logical change, may be expected to vary its amplitude in a slow 



r and irregular manner from decade to decade. The Eulerian 



^ motion, having a period of 427 days, ought to be nearly circular, 



NO. 1383, VOL. 53] 



unless the equatorial moments of inertia of the earth differ much 

 rnore than we can supjx)se probable. The annual motion may 

 differ somewhat from a circle, and be somewhat less regular. 

 There can be no strictly periodic changes in the latitude but 

 these two, but it is quite possible that, owing to secular changes, 

 or changes continued through several years, in the currents of 

 the ocean and atmosphere, corresponding changes of irregular 

 long period may be found in the latitude. 



It will be seen that these conclusions are accordant with 

 Chandler's results as regards the double period, but do not fully 

 agree with them in other details. Simon Newcomb. 



THE PAST, PRESENT, AND FUTURE WATER 

 SUPPL V OF LONDON. 1 



TN a discourse to the members of the Royal Institution on the 

 subject of the metropolitan water supply nearly thirty years 

 ago, I stated that out of every thousand people existing upon 

 this planet three lived in London ; and, as the population of 

 London has, in the meantime, doubtless grown at a more rapid 

 rate than that of the rest of the world, it will probably be no 

 exaggeration to say that now, out of every thousand people 

 alive on this earth, four live in London ; and therefore, any 

 matter which immediately concerns the health and comfort of 

 this vast mass of humanity may well merit our most earnest 

 attention. Amongst such matters, that of the supply, in 

 sufficient quantity, of palatable and wholesome water, is cer- 

 tainly not the least in importance. 



It is not therefore surprising that this subject has received 

 much attention from several Royal Commissions — notably from 

 the Royal Commission on Water Supply of 1867, presided over 

 by the Duke of Richmond ; the Royal Commission on River 

 Pollution and Domestic Water Supply of Great Britain, presided 

 over by the late Sir William Denison, of which I had the honour 

 to be a member; and, lastly, that of 1892, of which Lord 

 Balfour of Burleigh was the chairman. 



The Royal Institution has, for nearly three-quarters of a 

 century, been prominently connected with the investigation and 

 improvement of the metropolitan water supply ; no less than 

 four of our Professors of Chemistry have been successively 

 engaged in this work, namely Profs. Brand, Odling, Dewar, 

 and myself, whilst three of them have been members of the 

 Royal Commissions just mentioned. I may therefore perhaps 

 be excused for bringing the subject under your notice again for 

 the third time. 



On the present occasion, I propose to consider the subject 

 from three points of view, viz. the past, the present, and the 

 future ; and, for reasons which will appear hereafter, I shall 

 divide the past from the present at, or about, the year 1883, and 

 will not go back farther than the year 1828, when Dr. Brand, 

 Professor of Chemistry in the Royal Institution, Mr. Telford, the 

 celebrated engineer, and Dr. Roget, Secretary of the Royal 

 Society, were appointed a Royal Commission to inquire into the 

 quality and salubrity of the water supplied to the metropolis. 



The Commissioners made careful examinations and analyses, 

 and reported as follows. "We are of opinion that the present 

 state of thc'supply of water to the metropolis is susceptible of, and 

 requires, improvement ; that many of the complaints respecting 

 the quality of the water are well founded ; and that it ought to be 

 derived from other sources than those now resorted to, and 

 guarded by such restrictions as shall at all times ensure its 

 cleanliness and purity. (At this time the water was pumped 

 from the Thames Ijetween London Bridge and Battersea. ) To 

 obtain an effective supply of clear water free from insects and all 

 suspended matter, we have taken into consideration various 

 plans of filtering the river water through beds of sand and other 

 materials, and considering this, on many accounts, as a very 

 important object, we are glad to find that it is perfectly possible 

 to filter the whole supply, and this within such limits in point of 

 expense as that no serious objection can be urged against the 

 plan on that score, and with such rapidity as not to interfere 

 with the regularity of the service." 



Before the year 1829, therefore, the river water supplied to 

 London was not filtered at all ; but after the issue of this report 

 the companies set themselves earnestly to work to improve the 

 quality of the water by filtration. 



1 A discourse delivered by Dr. E. Frankland, D.C.U, LL.D., F.R.S., 

 at the Royal Institution on February 21. 



