NA TURE 



[June 27, 1901 



These alloys, after polishing, were prepared for photography 

 by slightly oxidising the surface by gently heating them in air, 

 the temperatures needed to bring out the pattern in this way 

 being far below those at which changes in the structure of the 

 alloy occur. When treated thus, the parts rich in copper 

 oxidise, and therefore darken, more rapidly than those rich in 

 tin, hence the dark parts in the photographs correspond to 

 matter rich in copper, and vice versa. 



owing to an unforeseen cause of error the measurements were 

 not trustworthy to the last place of decimals. However, when 

 care was taken to avoid this error, consecutive readings agreed 

 to less than this amount, showing that the method was capable 

 of greater accuracy than was required. Errors caused by the 

 growth of the roots of a tree near the stone, swelling of the soil 

 due to dampness, and the expansion of the rod from change of 

 temperature are discussed. 





The authors have found similar, though sometimes more 

 complex, phenomena throughout a considerable range of com- 

 position. The results lead to the conclusion that it is unwise 

 to interpret a freezing curve by the examination of slowly-cooled 

 alloys only. 



May 2.— "On the Small Vertical Movements of a Stone 

 laid on the Surface of the Ground." By Horace Darwin. 

 Communicated by Clement Reid, F. R.S. 



The experiments described in this paper were undertaken 

 originally to measure accurately the downward movement of a 

 stone caused by earthworms. The upward and downward 

 movements due to varying moisture of the soil and to frost were 

 found to be much larger than was expected. These movements. 



interesting in themselves, increase the difficulty of accurately 

 determining the movement due to the action of earthworms. 



To obtain a fixed point from which to measure the displace- 

 ment of the stone a rod was driven into the ground to a depth 

 of 2 '63 metres. The top of this rod was the point from which 

 all measurements were taken. 



A circular stone about 460 mm. in diameter and about 57 mm. 

 thick, weighing about 23 kilos., was placed on the ground with 

 the rod projecting through a hole in its centre. 



A screw micrometer graduated to "Oi mm. was used. The 

 screw was turned until its end just touched the end of the rod ; 



NO. 1652, VOL. 64] 



The movements of the stone are represented graphically ; the 

 figure reproduces one of the diagrams. 



The curve marked "Movement of Stone" represents the up 

 and down movements of the stone from February 19 to October 

 9, iSSo, due to the varying dampness of the ground. 



The points corresponding to each observation are surrounded 

 by a small circle ; their vertical distance apart is proportional to 

 the movement of the stone, each division of the scale represent- 

 ing I mm. ; the horizontal distance apart is proportional time. 

 The curve shown by the dotted line roughly represents the 

 dampness of the soil. Moisture is assumed to leave the soil at 

 a uniform rate ; the ordinates are proportional to the rainfall 

 less this assumed amount evaporated or drained away ; both 

 quantities are calculated from February 19. 

 The curves follow each other, showing that 

 the stone fell as the soil became dryer and 

 rose again with rain. In May there is a 

 marked exception ; the most probable ex- 

 planation is an error in reading the micro- ■ 

 meter. The total downward movement from 

 February 19 to September 7 is 5 '6 mm. On 

 another occasion artificially wetting the ground 

 raised the stone 0'6 mm. 



Measurements taken in the winters of 1S78 

 and 1 886 show that the stone sank about 

 2 '2 mm. per year. Measurements were also 

 taken in the summer of most years from 1878 

 to 1S96. The downward movement was not 

 regular, and it is shown that this also is par- 

 tially due to the varying dampness of the soil. 

 From 1S78 to 1887 the stone sank on the 

 average about 2 '3 mm. per year, and from 

 1S87 to 1896 about '36 mm. per year. 



The effect of frost is to raise the stone ; it 

 fell rapidly during a thaw — on one occasion 

 2 '3 mm. in 4 hours 40 minutes. 



June 6. — "The Measurement of Ionic 

 Velocities in Aqueous Solution, and the 

 Existence of Complex Ions." By B. D. 

 Steele, B.Sc, 1S51 Exhibition Scholar 

 (Melbourne). Communicated by Prof. Ram- 

 say, F.R.S. 

 The method of measuring ionic velocities described by Masson 

 has been extended in such a manner that, by the present method, 

 the use of gelatin solution and of coloured indicators is not 

 necessary. 



An aqueous solution ot the salt to be measured is enclosed 

 between two partitions of gelatin which contain the indicator 

 ions in solution, the apparatus being always so arranged that 

 the heavier solution lies underneath the lighter. On the passage 

 of the current the ions of the measured solution move away 

 from the jelly, followed at either end by the indicator ions ; the 

 boundary is quite visible in consequence of the difference in re- 



Ocl, 



