NA TURE 



[June 30, 1904 



uf colour is a secondary effect; in presence of radium tlie 

 diamond is extremely phosphorescent, and it continues to 

 shine during the whole time of the experiment. This 

 constant state of vibration in which the diamond was kept 

 for many weeks may have caused an internal change re- 

 vealing itself in a change of colour. Indeed, it is not 

 difficult to suppose that a chemical as well as a physical 

 miction may result. If the yellow colour is due to iron in 

 ihe ferric state a reduction to the ferrous state would quite 

 account for the change of colour to a pale blue-green. 



This alteration of colour may be of commercial import- 

 ance. If " off colour " stones can be lightened their value 

 will increase, while if the prolonged action of radium is 

 to communicate to them a decided colour they would be 

 worth much more as " fancy " stones. 



\.\ddcd June i6.— After the ten days' heating in the above 

 acid mixture the two diamonds were put together in a 

 i^lass tube and carried about for twenty-five days, some- 

 rimes loose and sometimes in the tube. They then were 

 laid near together on a sensitive film in total darkness for 

 twenty-four hours. On developing, diamond B had im- 

 pressed a strong image on the film, but only a very faint 

 mark could be seen where the other diamond had been. 

 Probably this slight action was due to a little radio-activity 

 induced in A during its twenty-five days' proximity to B. 



The experiment was then repeated for confirmation, 

 allowing the diamonds to remain on the sensitive surface 

 lor only five hours. On development, a good image of 

 diamond B was seen, but not so black as in the former 



The fact that diamond B was strongly radio-active after 

 it had been away from radium for thirtv-five days, for ten 

 of which it was being heated in a mixture powerful enough 

 to dissolve off its outer skin of graphite, seems to me proof 

 that radio-activity is by no means a simple phenomenon. 

 It not merely consists in the adhesion of electrons or eman- 

 ations, given off by radium, to the surface of an adjacent 

 body, but the property is one involving deep-seated layers 

 below the surface, and like the alteration of tint is prob- 

 ably closely connected with the intense phosphorescence the 

 stone had been experiencing during its seventy-eight days' 

 burial in radium bromide.] 



THE MARKINGS AND ROTATION PERIOD 



OF MERCURY. 

 jyj LiCH new light was thrown upon the rotation period 

 of Saturn during the year 1903, and it seems highly 

 probable that the next planet to afford us information as 

 to the same feature will be the planet Mercury. Spots of 

 very definite and distinct character are certainly visible on 

 the surface of this fugitive little orb, which offers a more 

 promising field for new discoveries than Venus, though it 

 is considerably smaller, at a much greater distance from 

 us, and more unfavourably placed for observation. The 

 markings sometimes perceptible on Mercury appear to be 

 of sufficient prominence to be followed, and if really capable 

 observers are forthcoming, at the opportune period, to study 

 them, It will be possible to ascertain once and for all whether 

 this circumsolar planet turns on its axis once in about 24 

 hours or 88 days, and an important advance in our know- 

 ledge will have been made. 



^ Spots have been discerned on Mercury since the time of 

 Schroeter about a century ago. Amoiig those who hava 

 obtained observations of them are the following ; — 



1882 

 1S82-3 

 iSg6 

 1896 

 1900 

 1904 



In 1800 Schroeter announced that the rotation period 

 was about 24h. 4m. from blunted appearances of the 

 southern horn, but doubted if the value could be determined 

 to within a few minutes. In 1801 Harding perceived a 

 dusky spot in the southern hemisphere, and derived the 

 period as 24h. 5m. 30s. Further observations, however, 

 obtained by himself and Bessel caused him to reduce this 

 period to 24h. om. 50s. Bessel found 24h. om. 53s. from 

 l" 



NO. 1809, VOL. 70] 



several of Schroeter's observations extending over fourteein 

 months. In 1882 Denning, at Bristol, thought a period 

 of. about 25 hours would satisfy the observations, but 

 Schiaparelli, in the pure Italian sky, arrived at very different 

 results, and concluded that the planet rotated in 88 days, or 

 in the same period as he revolved round the sun. Quite- 

 recently McHarg found the time 24h. 8m. from his own 

 observations of a dark spot in -April, 1904. He also de- 

 duced a period of 24h. 5m. 4SS. from a blunting of the 

 southern horn seen by Schroeter in iSoo .March, and by 

 Denning in 1SS2 November. 



ON THE DIMENSIONS OF DEEP-SEA WAVES, 

 AND THEIR RELATION TO METEOR- 

 OLOGICAL AND GEOGRAPHICAL CON- 

 DITIONS.' 

 "T^HE following table has been compiled from the original 

 sources after re-calculating the true velocities corre- 

 sponding to the " Beaufort numbers " in accordance with 

 the alteration of reduction factor adopted by meteorologist& 

 since the date of the observations : — 



Tabic showing the Relation between the True Velocity of 

 the Wind in Statute and in Geographical Miles per Hour 

 and the Height of the Wave in Feet, as deduced front 

 Observations by numerous French Observers cxtendini^- 

 over many years and taking in all the Oceans. 



2-01 



2-41 

 2-19 



1-97 

 I 61 



2 J I 

 1-91 

 243 

 1-89 

 2-20 

 2-31 

 2-38 

 2-13 



2-24 

 2-05 

 2-04 

 222 



Average 2-03 



0-86 



1 -46 

 177 

 1-75 



2 eg 

 I 89 

 I -71 

 1-41 



2-01 



I -65 

 21 1 

 ■•65 

 1-91 

 2 or 

 2-07 

 ■ 85 

 '■94 

 178 

 177 

 I '93 



1-78 



This table gives the average of many hundreds of days' 

 observations conducted at various times during a period 

 of about forty years by independent observers, all French 

 seamen of the navy or merchant service, carried out in 

 almost all parts of the oceans ordinarily visited by ships, 

 and from many different vessels (none, however, of the 

 great size of our modern liners, and therefore better for 

 such observations), and shows the average height of the 

 wave, in open sea with sufficient depth of water, to be in 

 simple arithmetical proportion to the velocity of the wind. 

 the height of the wave in feet being in round numbers one- 

 half of the velocity of the wind in statute miles per hour. 



This result does not express a dynamical law ; it is simply 



1 Extracted from a paper by Dr. \'aughan Cornish in the ^U-cgraphLai^ 

 Journal for May, 1Q04. 



