470 



NOTES AND MEMORANDA. 



in the case C. By means of a circular contact-breaker F, Fig. 7, 

 fixed to the spindle D, but insulated from it, the current is only 

 allowed to excite the magnet when its poles are at the foot of any of 



Fia. 



the inclined armatures ; as it tui us towards the top, or point nearest 

 its poles, the current ceases, and with it any retarding action upon 

 the magnet. Acquired momentum carries it to the foot of the next 



incline, and the process is repeated, a steady rotary motion resulting, 

 which can be regulated by exposing more or less of the zinc in the 

 battery to chemical action. 



English Microscope for Students of Mineralogy and Petrology. 

 — Mr. Frank Eutley describes * a new Microscope, specially suited 

 for mincralogical and petrological research, constructed for him by 

 Mr. T. W. Watson, of Pall Mall. 



An examination of one of the Microscopes devised by Professor 

 Eosenbusch and manufactured by Fuess, of Berlin, showed that, 

 although that instrument possessed many features of great merit, it 



* 'Nature,' xx. (1879) 13. 



