696 



SCIENCE. 



[N. S. Vol. III. No. 71. 



from A and cast a shadow, moderately well 

 defined, of the plate B. 



3. B was made the cathode and C the 

 anode. An iron washer was placed in con- 

 tact with the thin aluminum window at B. 

 The resulting photograph is given in Fig. 4. 

 it shows that the X-rays radiate from A ex- 

 actly as in (2), casting a shadow of the 

 aluminum disc and the iron washer in front 

 of it. 



Now, while it is possible to explain ex- 

 periments (1) and (2) by considering that 

 the X-rays radiate from the anode, no such 

 explanation will account for experiment 3, 

 in which the undoubted source (A) was un- 

 connected with either terminal of the sec- 

 ondary coil which furnished the discharge. 



On the other hand, not only are all three 

 experiments consistent with the statement 

 given above, but the origin of the X-rays 

 at the place where fluorescence is excited 

 on the glass walls of the common form of 

 Crooks tube is also thereby accounted for. 



While it may be true that the effects may 

 be enhanced by making the anode the first 

 object encountered by the cathode rays, the 

 result of these experiments is to show that 

 the anode does not play an important role 

 in the phenomenon. 



A. A. MlCHEMON, 



S. W. Steatton. 



CURRENT STUDIES IN EXFERUIENTAL 

 GEOLOGY. 

 THE COLOR OF WATER, AS AFFECTED BY CON- 

 VECTION AL CURRENTS. 



Prof. W. Spring, of Liege, has just 

 added a new and interesting contribution* 

 to our knowledge of the causes of illumin- 

 ation of deep waters. Pure water is ac- 

 tually blue when seen through sufficient 

 thickness. Spring showed in 18S3 that per- 

 fectly colorless particles in suspension would 

 form a turbid medium, giving passage to 



* Arch, des Sciences phys. et nat. Geneva, March, 

 1896. 



