432 



Scientific Intelligence. 



The union is instantaneous and complete, and the depth of the amal- 

 gamation is easily regulated by the quantity of mercury suffered to 



remain in contact with the zinc. 



This method is applicable even when the zinc is thoroughly oxydized 

 on the surface ; but if it has been previously used in a galvanic battery, 

 it is best to cleanse the surface first by immersion in somewhat con- 

 centrated hydrochloric acid. 



A set of Grove's cylinders thus amalgamated, it is stated, have been 

 used at Miami University during a long course of lectures without 

 serious injury and without re-amalgamation. 



8. A Magneto-Tangential Machine, (in a letter from Prof. O. N. 

 Stoddard.) — The instrument, a description of which is given below, 

 was invented during the winter of 1848, while engaged in a course of 

 lectures upon galvanism, and was intended to exhibit the tangential 

 force of a magnet. As originally constructed, the brass ring within 

 which the spindle revolves, was attached to the top of a wooden cup. 



For the present modified form which dispenses with the cup, the 

 writer is indebted to the suggestions of Dr. Locke of Cincinnati. 



a. An upright pillar or rod of 

 metal. 



b. A permanent magnet from 4 

 to 6 inches in length, and 

 diameter. 



c. Arm to support the magnet. 



d. A ring of brass attached to 

 the upright, 2J inches in diameter, 

 and i in width, the inner surface 

 beveled, making; the lower diame- 



inch in 



ter \ inch less than the upper. 



e. A spindle of copper or brass, 

 3 inches long and about -j- 1 ^ inch 

 thick, with a circular disk (g) of 

 the same metal 



m inch in diameter. The spindle should be carefully 

 turned, and the lower end reduced to a fine point. 



h. A cup of brass in which the spindle rests. 



Z, k. Mercury cups, one connected through the upright (a) with the 

 Ting (d), the other with the cup (h). As the spindle°rests on a fine 

 point, while its disk rolls on the inside of the ring, it revolves with the 

 application of a very slight force. 



If one or two drops of mercury be placed in the cup (*fc a free 

 passage is afforded for the battery current from one mercury cup, 

 through the spindle ring and upright, to the other. 



The current is not broken by the revolution of the spindle as its 



disk 



is constantly in contact with the ring. On connecting the instru 



meat with a battery, the spindle revolves rapidly around the magnet. 

 With a small battery of copper and zinc, it has made two hundred and 

 fifty revolutions in a minute, and with a few cups of a Grove's battery, 

 more than three hundred. 



