Sinnott and Bartlett — Coniferous Woods. 293 



Fig. 13. Eadial section, showing the shallow medullary rays. 



Fig. 14. Eadial section, showing the usually distant bordered tracheid 

 pits, in a single row, and the pits between ray and tracheids. 



Fig. 15. Tangential section, showing in cross section the very low medul- 

 lary rays and the pits of the radial walls of the tracheids. 



Fig. 16. Transverse section of the pith. 



Fig. 17. Transverse section, showing a row of traumatic resin canals. 



Fig. 18. Eadial section, showing parenchyma and tyloses of a traumatic 

 resin canal. 



SCIENTIFIC INTELLIGENCE 



I. Chemistry and Physics. 



1. The Density of Lead from Radioactive Minerals. — Theo- 

 dore W. Richards and Charles Wadsworth, 3rd, have studied 

 this matter on account of the startling differences that have been 

 observed by several investigators in the atomic weight of lead 

 from radioactive sources ; for these differences suggest that other 

 properties may vary in different specimens, and the comparison 

 of these may be of service in tracing the true causes of the differ- 

 ences in atomic weights. The authors observe that the phe- 

 nomena are of interest whether or not the plausible hypothesis of 

 Soddy and Fajans concerning the " isotopes " is accepted. They 

 describe a special stoppered pycnometer that was used for the 

 work, and give details of the very careful methods that were 

 employed for purifying the samples of lead. Two samples of 

 ordinary lead and one of radioactive lead of Australian origin 

 were used. The latter was taken in two states of purification. 

 The following average results were obtained at 19*94° C. : 



Density of ordinary lead 11 *337 



Density of radioactive lead 11 "288 



Density of same, further fractionated.. 11-289 



The density of radioactive lead is thus found to be 0*049, or 0*43 

 per cent lower than that of ordinary lead, a very striking differ- 

 ence. It is interesting to notice that the atomic volume of the 

 Australian radioactive lead is practically the same as that of ordi- 

 nary lead, for the atomic weights, as they have been determined, 

 are respectively 206*3 and 207*3, so that the atomic volumes 

 (206-3/11-288 and 207*2/11*337) are 18*276 and 18-277. Of course, 

 no one knows as yet what proportion of impurity exists in the 

 radioactive sample, which doubtless contains some ordinary lead, 

 but if the atomic weight of the pure " isotope " is really 206, this 

 sample must have consisted chiefly of the isotope. On the other 

 hand, it is possible that the theory is incomplete and that the 



