SCIENTIFIC SUMMARY. 
339 
Staid, that 38,000 dollars is the estimate for labour and lighting of the city 
street lights. The labour and the amount of gas that would be saved in the 
time allowed for lighting and putting out, and the amount that is now used 
on bright moonlight nights, constitute an aggregate which no doubt would 
more than pay for the whole expense of introducing the improvement for 
the first year. 
An Improved Voltastat. — ^At the meeting of the Chemical Society (April 
16), Professor Guthrie described and exhibited an ‘^Improved Voltastat,” 
by which the cm-rent of a galvanic battery may be maintained perfectly 
constant and regular by a self-acting arrangement, which will become in- 
telligible by the following description : — A vertical glass cylinder of about 
the size of a test tube is charged with dilute sulphuric acid, with a layer of 
mercury below occupying about one-third of its total contents. Partly im- 
mersed in the acid liquid is a pair of platinum electrodes insulated by glass 
fused upon the wires at that portion which passes through the cork stopper 
of the jar, and a comparatively wide glass tube, open at both ends, is fixed in 
the same cork, with its lower extremity dipping below the level of the 
mercury, whilst another delivery tube with bulb and capillary orifice pro- 
vides for the slow escape of the mixed gases resulting from the electro-de- 
composition of the water. This apparatus having been placed in the battery 
circuit, say of three Bunsen cells, evolves the oxyhydrogen gas with a ra- 
pidity which may be easily regulated by the size of the aperture ; if, then, 
the activity of the battery is increased, the larger volume of gas, unable 
to escape, exerts a greater degree of pressure upon the liquid contents of 
the cylinder, and the mercury is forced up the open tube, whereby the 
column of liquid descends and smaller surfaces of the platinum plates are 
left immersed, and the power of conduction is to a corresponding extent 
lessened. In this manner the author states that he found no difficulty in 
maintaining a perfectly uniform current for a period of six or seven hours, 
and any required adjustment could be made either by altering the size of 
the apparatus or of its component parts. By collecting the gases evolved 
this little arrangement could also be made to serve as a voltameter. 
Can Electricity travel through a Vacuum‘d — This is answered in the 
negative by the results of recent inquiries. M. Alvergniate, of Paris, has 
constructed a new apparatus for proving that electricity cannot pass through 
an absolute vacuum. Two platinum wires are inserted into a tube so that 
their free ends are within about one-eighth of an inch of each other. The 
air is then exhausted from the tube by means of a mercurial column, after 
which the electric spark will not pass from one wire to the other. 
Relation of Magnetism to Atomic and Specific W 3ight. — In a paper pub- 
lished in a late number of the American Journal of Mining, by Dr. P. H. 
Van der Weyde, the author establishes some very interesting points in 
physics. He says, ^AVhen we divide the specific gravity of the different 
metals, respectively, into their atomic weight, we obtain quotients, which 
indicate relatively the position of their actions.” He then shows that these 
quotients have a very remarkable relation to the magnetic properties of the 
metals, and he supplies a long and useful table of reference. The following 
are a few of his observations, that may show the interest of the subject in- 
quired into. 1st. The five magnetic metals have all quotients below 4. 
