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POPULAR SCIENCE REVIEW. 
bicipital groove, and afterwards at the wrist, where it runs on the ulnar side 
of the musculus flexor carpi radialis, the distance of the electrodes being 
about 300 millimetres, or above one foot. The muscular contractions pro- 
duced were strong, a more powerful current being required for the excita- 
tion of the nerve above where it lies deepest. In order to obtain trust- 
worthy results, one or two minutes were allowed to pass between each 
experiment. The best observations gave a result of from 50 to GO metres per 
second as the rapidity of propagation of motor impulses, with a mean of 
53 metres per second. This differs considerably from the estimation of 
Helmholtz, who estimates it at only 33 metres per second. The point of 
excitation in Helmholtz’s experiments was somewhat higher than in those 
of M. Place ; and when Helmholtz’s point was taken, a number (35*25 
metres per second) not very different from his was obtained. Further 
investigations showed the general truth of Munk’s observation, that the 
rapidity of propagation of impulses was much greater in the peripheral than 
in the central portions of a nerve. Helmholtz’s observations were earned on 
with a new instrument, of which the idea was suggested by Fick. He 
found that variations in temperature exert an important influence on the 
rapidity of propagation of motor impulses, the rapidity being much greater 
in warm than in cold temperatures. He found also that when two induc- 
tion-currents are passed through, an interval of at least l-500th of a second 
must elapse between them in order that the second stroke should produce 
an augmentation of the muscular contraction. If the period be less than 
this, the two act as a single shock ; with an interval of l-300th of a second 
the augmentation is very perceptible. Constant currents readily produce 
tetanus, especially when passed in a downward direction. Oscillations are 
felt in the muscle, the duration of which amounts to 0*09 of a second. 
METALLURGY, MINERALOGY, AND MINING. 
u Mineralogical Notices ” was the title of a paper read before the Royal 
Society on November 17, by Professor Maskeyne and Dr. Flight. It deals 
with several minerals, and we may mention a few of them. The first is 
u On the Formation of Basic Cupric Sulphate.” In 1867 M. Pisani described 
a mineral which he supposed to be the Woodwardite of Mr. Church. The 
substance, however, is not the latter mineral. It had previously been ex- 
amined in the laboratory of the British Museum, and the results sufficiently 
tallied with those of M. Pisani to identify the mineral. It can be divided 
into an inner layer and an outer crust, of which the contents were given. 
2. An opal from the Waddela Plain, Abyssinia. Mr. Markham presented to 
the British Museum some remarkable specimens of green opal from the 
above locality. An analysis is given of it. Next follow Frankolite from 
Cornwall; Epidote and Serpentine from Iona; Cronstedtite , Pliolerite, and 
others. The paper is reported in the 11 Chemical News ” of November 25. 
Steel Rails.— There are in the United States, says the “ Philadelphia 
Ledger,” 46,000 miles of railway which it is necessary to re-lay with steel 
rails. It takes 100 tons of rail to lay a mile of road. The estimation of 
