538 Farwell and Stifler — Common Laboratory Experiments. 



side of the plane, sliding along on a planed surface as the 

 plane is lifted. As B is moved away from the hinge the plane 

 is steadily raised, and will rest securely in any position. The 

 screw and lever system operates easily, a weight of 30 pounds 

 or more on the end of the plane having been lifted with little 

 effort. 



The annoyance of the usual arc for measuring the angles is 

 avoided by using a steel scale to determine the height of the 

 plane. In determinations of the angle of repose the plane is 

 very easily operated, and the adjustments can be made quickly 

 from any position. The iron base permits the attachment of 

 pulleys or other devices without in any way interfering with 

 the operation of the plane. 



Columbia University, 

 Jan. 15, 1913. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. Radio-elements and the Periodic Law. — Frederick Soddy, 

 some time ago, pointed out that in several cases when the a-par- 

 ticle was expelled the atom passed from a family of even number 

 in the periodic table to the next lower numbered even family, the 

 family of odd number being always missed. Further, in the 

 changes in which the a-particle was not expelled the atom in sev- 

 eral cases reverted to its original group, resulting in a curious 

 alternation of properties as the series proceeds. Now, when this 

 occurs, an element of the fourth family, for example, expelling 

 an a-particle and becoming a member of the second family, 

 which after further changes reverts to the fourth family, the two 

 representatives of the fourth family so resulting are not merely 

 similar in chemical properties, but although one of them has lost 

 an a-particle (helium) and has its atomic weight diminished by 

 four units, they are non-separable by any known process. This 

 applies not only to the disintegration products of a single series, 

 but to all the products. Thus, in the fourth group, thorium, 

 uranium X, ionium, radio-thorium, and radio-actinium are all 

 chemically non-separable, though they result from three separate 

 series, and the calculated atomic weight varies from 234 to 228. 



A corollary to Soddy's rule for radio-active changes has been 

 advanced by A. S. Russell. This states that when a /3-ray or 

 rayless change occurs the atom passes into the family of the 

 periodic table next higher in number, that is, the change in these 



