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and give the following tabulation as the correct expression of the relative value of several lights examined, in which the intensity increases with the figures:

Relative Chemical

Energy. Drummond-light .....

3
Zinc burning in oxygen..

4
Magnesium lamp..
Flame of nitrous oxide and carbon-disulphide vapor..

6
Flame produced by leading nitrous oxide into that of carbon-
disulphide burning in an open dish........

6-7 Flame produced similarly by oxygen...

7 Oxygen directed upon the flame of burning sulphur.

8

5

From the foregoing it appears that the light produced by the combustion of sulphur in oxygen is possessed of extraordinary chemical energy, and may be applied to photographic uses with excellent effect.

Stein, in a communication upon the subject of normal weights and measures of rock-crystal, remarks that Kekulé pointed out, some time ago, the fact that all amorphous bodies, whether produced by casting, rolling, hammering, or stamping, are possessed of the tendency to go over into the crystalline condition. The molecules of such substances he regards as being in abnormal positions relative to each other, and the striving toward crystallization is the natural effort to assume the position of equilibrium. For these reasons, Kekulé objected to normal weights and measures made of metal, affirming that they could not be relied upon to remain constant; while, on the contrary, this objection would not hold good of such normals when constructed of a crystallized substance, as, for example, of rock-crystal. Recognizing the validity of the foregoing arguments, the author has had such weights and measures cut at Oberstein. To produce the measures, the pieces are cut exactly parallel with the optical axis of the rock-crystal, so that the main axis of the crystal coincides with the median line of the rod. The same rule is likewise observed with the weights, by which an unequal expansion is avoided. These normal weights and measures are manufactured at Oberstein by II. Stern, who has likewise devised a method of attaching the pieces to each other, when measures of considerable length are required, in such a manner that any alteration of the

mum.

scale of parts is not possible, and the correctness of the division, as also of the total length, may be under control. For these weights and measures a number of advantages are claimed. The considerable hardness of the rock-crystal (7) protects the weights from abrasion by usage, to which objection all weights of metal are open. The rock-crystal is even more indifferent to the action of acids and alkalies than platinum, while it is utterly indifferent to oxidation, to which weights of metal are more or less liable. Moisture has no effect upon it, since it is not hygroscopic. Rock-crystal, as compared with the metals, has a very small co-efficient of expansion, on which account the errors arising from variations of thermometer and barometer are reduced to a mini

The weights are not objectionable on the score of expense, their cost being quite moderate. As produced by Stern, the larger weights, from 50 grammes to 1 gramme inclusive, are made of rock-crystal, the pieces having the same form as the commonly used weights of gilded brass, while the weights under 1 gramme are made as usual of platinum. Fresenius, who has examined and employed them, declares them to be admirably adapted for analytical work.

Lewin impregnates sandstones with a solution of sulphate of alumina, which he follows with water-glass. The stones thus impregnated may be polished and appear like marble. They resist the action of fire and of the atmosphere, and are well adapted both in appearance and durability to take the place of marbles. By preparing them at a high temperature the stones take on a species of glaze, which may be decorated with a variety of colors to imitate colored marbles and the like,

ANNUAL RECORD

OF

SCIENCE AND INDUSTRY.

1875.

A. MATHEMATICS AND ASTRONOMY.

THE EARLY USE OF THE DECIMAL POINT. Mr. J.W.L. Glaisber, in some remarks on the history of the introduction of the decimal point into arithmetic, concludes that this invention must be attributed to Napier, the immortal inventor of logarithms. The earliest work in which the decimal separator was employed seems to be Napier's posthumous work in 1619, at wbich time it appears that he was aware of all the attributes that enable the decimal point to complete systematically our method of notation. About the same time Briggs employed a bent or curved line, for which, in printing, he substituted merely a horizontal bar drawn under the figures that were to be considered as decimals; but Napier himself has left so many instances of the actual use of the decimal point as to render it pretty certain that he thoroughly appreciated its use.- Rep. Brit. Assoc., 1873, 12.

TABLES OF ELLIPTIC INTEGRALS. The committee of the British Association, which has for some years had in hand the preparation of a list of tables and the calculation of new mathematical tables, report the completion of the tables of the elliptic functions, on which six or seven computers have been constantly engaged for two years past, under the superintendence of the Messrs. Glaisher.

A

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