264 Dr. Schuster on 



the curve of solar activity can be best represented as a super- 

 position of three oscillations, one of ten-and-a-half, one of 

 twelve, and a minor one of about sixteen years. The irre- 

 gularities would thus be produced by the beats of these 

 three fluctuations. It will be interesting to see how far 

 further observation will confirm this result. 



It was in great part owing to Balfour Stewart's influence 

 that a Committee of the British Association was formed at 

 the Canada meeting, " to consider the best means of com- 

 paring and reducing magnetic observations." He was 

 appointed secretary to the committee which has already 

 presented three valuable reports. They contain among 

 other matters a research jointly with Mr. Lant Carpenter 

 on the connexion between magnetic disturbances and the 

 strength of the wind. A good case is made out from the 

 conclusion that high and low disturbance values of magnetic 

 force correspond with, and slightly precede, high and low 

 wind values. 



Balfour Stewart was the author of several text-books.. 

 His "Primer of Physics," as well as his "Elements of 

 Physics," are well established as sound and clear elementary 

 works. His book on heat is an excellent treatise, and his 

 " Lessons in Elementary Practical Physics," written jointly 

 with Mr. W. W. Haldane Gee, is the most complete compo- 

 sition of experimental methods in physics which has been 

 written. An admirable treatise on the " Conservation of 

 luiergy," forms one of the volumes of the International 

 Science Series. Students of Terrestrial Magnetism will for 

 a long time to come value the clear and, at the same time 

 full account he has given of the present state of the subject 

 in the last edition of the " Encyclopitdia Britannica." His 

 book "The Unseen Universe, or Physical Speculations on 

 a Future State," by Stewart and Tait, was published 

 anonymously at first. It went rapidly through several 

 editions, and in the fourth the authors' names were given. 



