April 29, 1886] 



NATURE 



615 



ponderating ; we may conclude '.hat the latitude at which the 

 change of phase takes place shifts with the season, and that its 

 average position is not far south of Lisbon. 



The good agreement of our formula with the observed facts 

 encouraged me to deduce the vertical component of force. 

 Measured downwards it should be 



sin 2u sin (/ 4- K) 

 if the cause of the disturbance is outside the earth, but 



- f sin 2u sin {t + A.) 

 if the cause of the disturbance is inside the earth. 



Both expressions have their maxima and minima coincident 

 with those for the northerly components of horizontal force, a 

 fact which finds its CDnfirmation in actual observation. They 

 also show the phase of the vertical force to be the same for each 

 hemisphere and not to change as with the horizontal force. But 

 theieis an important distinction : while the vertical force has its 

 maxima and minima coincident with the maxima and minima of 

 horizontal force at latitudes greater than 45°, in the equatorial 

 regions the maximum of horizontal force ought to be coincident 

 with the minimum of vertical force, and vice versti, if the cause 

 is outside the earth's surface ; the opposite should be the case if 

 the cause is inside. 



At Greenwich the maximum of northerly force takes place at 

 7 p.m., the minimum at noon ; the maximum of vertical force 

 takes place at 7 p.m., the minimum at 11 a.m. 



At Bombay the maximum of northerly force takes place at 

 II a.m., the minimum at 9 p.m. ; there is a very decided mini- 

 mum of vertical force at II a.ni ; but there is no pronounced 

 maximum ; two minor maxima occur, one at 6 a.m. and the 

 other at midnight. 



As far as these results go they give an emphatic answer in 

 favour of the supposition that a great part at any rate of the 

 disturbing currents lie outside the earth's surface, a view which 

 Prof. Balfour Stewart has oflen supported in the last few years. 

 The results seem to me very encouraging, and I hope soon to 

 be able to make use of more material and to obtain more 

 accurate expressions for the various forces concerned. 



If we make use of the actual observations of Bombay and 

 Greenwich, we may calculate for each hour the intensity and 

 direction of the currents which would produce the disturbance. 

 This has been done, and the results have been collected in a 

 table. 



It is very remarkable how very nearly at the same local hours 

 tlie currents flow north and south at Bombay and at Greenwich, 

 namely, at 4 in tlie afternoon and between 7 and 8 in the morning. 

 It is curious, moreover, to find how very quickly the current 

 turns through the meridian ; at Bombay, at 3 o'clock, it flows at 

 an angle of 15° from the east, and at 5 already it flows due 

 west, and remains almost unaltered in direction till 5 o'clock in 

 the morning. At Greenwich the currents turn much less 

 sharply, but they always flow east when the currents at Bombay 

 flow west. Tlie system of currents indicated is that approxi- 

 mately shown by the equations given in the paper, the phase, 

 however, being different. Along the meridian on which the 

 local time is 4, the currents flow from the equator towards the 

 north ; tliey turn round in our latitudes towards east and west, 

 join on either side again to go south, where the local time is 

 7.30 in the morning, and come back along the equator. 



The strength of the currents is approximately of the same 

 order of magnitude as the currents we are accustomed to send 

 through our vacuum-tubes, but as the thickness of layer through 

 \\hich they are distributed must be very large compared to that 

 on which we experiment, the current-intensity at each place is 

 very small, far too small to cause luminosity. The currents, on 

 the whole, are weaker at Greenwich than at Bombay, but, while 

 ihey almost vanish at one time at Bombay, making the ratio of 

 the strongest to the weakest current equal to 73, that ratio is 

 only 3i at Greenwich. The minimum at Greenwich in the early 

 morning is as pi-onounced as the afternoon minimum, but much 

 less so at Bombay. 



On the whole, the numbers, both as regards direction and 

 intensity, show such a remarkable regularity that there is good 

 hope of obtaining a good mathematical representation of their 

 distribution. 



CHEMICAL AFFINITY AND SOLUTION 

 T N 1878 I read a paper to the Royal Society of Edinburgh, in 



which I stated my opinion, based on the results of a con- 

 siderable number of experiments, that chemical combination 



solution and suspension of solids, such as clay, in water differ 

 in degree only, and are manifestations of the same force ; and 

 that there seems to be a regular gradation of chemical attraction 

 from that exhibited in the suspension of clay in water up to that 

 exhibited in the attraction of sulphuric acid for water, which we 

 call chemical affinity. Further, I stated that the attraction of 

 chemical affinity is not, in all cases, at any r.ate, exhausted when a 

 definite compound is formed, but has sufficient power left to 

 form solution or suspension compounds. In 1881 I read another 

 paper on chemical affinity and atomicity, in which I went a 

 step further, and endeavoured to show that the theory of valency 

 as usually held was incorrect in assuming chemical affinity to 

 act in units or bonds, and insufficient to account for the various 

 phenomena of varying atomicity, or valency, molecular com- 

 pounds, crystallisation, solution, alloys, &c., and that all these 

 varied phenomena were simply due to the chemical affinity of 

 the elementary atoms, and that the difficulties disappeared if we 

 got rid of the idea of the indivisible units of chemical affinity, 

 and considered it as a whole acting all round, and spreading 

 out, so to speak. 



As an illustration of my views, I considered the compounds, 

 HCI, NII3, and NH4CI. In HCl we have two monovalent 

 elements combined, and their chemical affinities completely 

 neutr.alised or satisfied. In NH3 we have N considered as a 

 trivalent element satisfied with three monovalent elements. 

 Now these two completed, neutralised or satisfied compounds 

 combine with one another to form the third compound, NH^CI. 

 How is this ? The usual answer is that N sometimes acts as a 

 pentavalent atom, and in this particular case does so, and the 

 compound is represented graphically thus : 



H 



I 

 H— N— H 



/\ 



n ci 



I pointed out that this explanation was most unreasonable, 

 and to me, indeed, incredible, because it supposes that N, which 

 has usually such a weak affinity for CI, can nevertheless decom- 

 pose the HCI into its constituent atoms, and fix the atom of 

 CI to itself. While on the other hand the CI leaves the H, for 

 which usually its affinity is so great, and itnites itself to the N, 

 for which usually its affinity is so small, and this while the atoms 

 are in such close proximity, as they must be in a molecule, and 

 with so many hydrogen atoms allied with it. My explanation 

 was simply this. The affinity of the CI acts on all the four 

 atoms of H, and the affinity of the N does the same ; and thus 

 the whole molecule is held together, and may be represented 

 thus : 



/ "\ 

 N<H H>C1 



\ H / 



I did not, however, exclude the idea that the CI and N react 

 on one another to some extent, but the main cause of the com- 

 bination is as stated above. 



Since these papers were read chemists seem to me to be coming 

 more and more to my views in this matter. Thus Pattison 

 Muir in his " Chemical Principles," says : "It seems to me that 

 a most important step will be made if the bond theory of 

 valency is generally abandoned ; with it will go all those quasi- 

 dynamical expressions, the offspring of loose and slipshod ways 

 of thinking which have gathered round that strange anomaly, a 

 unit of affinity employed as a variable standard for measuring 

 nothing." Further, he says, in reference to the behaviotir of 

 acetic acid vapour when exposed to a high temperature; "If 

 this is so, we evidently have a series of substances beginning 

 with solution of salts or gases in water and proceeding through 

 crystallisation and acetic acid vapour at low temperature, 

 which connects mechanical mixtures on the one hand with stable 

 gaseous compounds on the other." 



Again, Professor Armstrong, in his address to the Chemical 

 Section of the British Association at Aberdeen last year, says 

 that in his view molecular compounds are held together by what, 

 for want of a better name, he calls surplus, or residual affinity. 

 In view of these and many other similar expressions of opinion, 

 all tending in the same direction, I may perhaps be excused for 

 again bringing forward the subject. 



