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POPULAR SCIENCE REVIEW. 
is 2-6 horse-power, so that only a small margin is needed to suffice for the 
greatest demand. 
5. The maximum energy which can he injuriously transformed into 
heat in the machine itself is T3 horse-power, so that there is no fear of de- 
stroying insulation in the helix by excessive heating. 
6. The approximately maximum current is habitually used, so that the 
commutator and collecting-brushes are quite capable of transmitting it. 
The new machine gives steadier light, with greater economy of power, is 
less liable to derangement, and may be driven without change of speed by a 
smaller engine, and is free from all objection when used for electro- 
deposition. 
It enables the author to effect an important simplification of the lamp 
regulator, dispensing with all wheel and clockwork. 
A New Zinc- Carbon Battery , patented by Mr. R. Anderson, is excited 
by means of hydrochloric acid, bichromate of potash, and certain other 
* salts.’ It may be used either with or without a porous pot. It is stated 
to have an E.M.F. of 2T5 Volts, to be free from local action, from internal 
resistance, and to be very constant. 
Toughened Glass appears to be less easily penetrated by the spark of the 
induction coil than that of the ordinary description. Ducretet, to whom 
the observation is due, proposes to utilize it for the production of Leyden 
jars and condensers. 
Rotation under the Barth's Magnetic Influence is found by Sig. Agostini 
to occur in a drop of mercury when an electrical current is sent vertically 
through it. If such a drop be placed on the pole of a steel magnet, to 
which one terminal of a weak battery is attached, and the other terminal 
introduced into the drop, it also undergoes rotation. In this manner the 
distribution of magnetism in bars, and the neutral points, may be studied. 
The motion is rendered visible by strewing lycopodium on the mercury. 
A New Galvanometer has been brought before the Physical Society of 
Paris by M. Marcel Deprez. It consists of a series of soft iron needles 
suspended between the limbs of a steel horse-shoe magnet of great power. 
Parallel to these needles are wound a few coils of stout wire to conduct the 
current. It is adapted to measure currents of considerable strength. 
Influence of Heat on Tuning-forks has been measured by Rudolph 
Konig. He finds that up to 50° or 60° C. it is practically constant. 
Thick tuning-forks are more influenced than thin ones of the same pitch, 
showing that change of elasticity, and not change of length in the prongs, 
is the efficient cause of the alteration. The influence on forks of different 
pitch is proportional to their vibration-numbers. Generally the period is 
changed by a difference of 1° Centig. The change in pitch of the 
normal C 3 = 512 vibrations per second at 20° for 1° Centig. is 0-0572 vibra- 
tion. Konig has constructed a compensated fork, which at any temperature 
gives exactly 512 vibrations. 
Variations from Mariotte’s Law have for some years occupied the atten- 
tion of Mons. Amagat, who has succeeded in making exact measurements of 
the changes in volume of gases when submitted to the pressure of a column 
of mercury over one-fifth of a mile in height. He has committed the 
results to the Annales de Chemie et de Physique. The place chosen for the 
