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Precautions in comparing weights
62
15'ec(mtiorts in Comt)aring lVeigh~. [Jour. Frank. Inst.,
Irrigation by the T a g u s . - - A proposal has been laid before the Portuguese Government to build a dam across the river Tagus, about 20 kin. (12"43 miles) above A1)rantas, in order to raise the level sufficiently to irrigate about 400,000 trueus (988,657 acres) of the adjoining lands. The expense would be very small in colnl)arlson with the increased value of the land, which is estimated at 600,000,000 francs ($120,000,000), or nearly one-third of the Portuguese national debt. African l~ailway.--Dul)on('hel's 1)rqieeted railway tbr connecting Algeria with Soudan continues to excite" great interest in l?ranee. A commission of 65 members has been al)i~ointed , and divided into four sub-commissions. The first, under the presidency.of de Lesseps, is to collect statistical and eeonomlcal intbrmation; the second, under Duponehel, is devoted to technical studies and the determination of routes; the third is to have charge of the explorations, and the fourth will consider international questions, especially with reference to the Moors, the Tripolitans and the Toncuezs. Many of the senators and deputies, who are members of the commission, have visited Algeria in order to understand the different projects which arc to be brought before them.-- Les .Mondes. C. Precautions in Comparing Weights.--Deville and Mascart, in explaining the construction of' the international geodetic standard, give an interesting account of some of the necessary precautions: During the long series of operations upon which a comparison of two weights is based, a balance should never be opened. Its cage, composed of two envelopes of glass, bordered with cloth, should be guarded from the external air, which would change the hygrometric state of the interior, and which would introdnee dust. The particles of dust notch the knife-edges, and change the velvet linings of the weight-boxes into a material comparable to emery-paper. Air may be forced into the interior, at the rate of 4 or 5 litres (4"227 or 5"283 qts.) per hour, being first deprived of dust by filtration through cotton, and dried by chloride of potassium or other dessicatives. The substance which seems to produce the least wcar on alloys of platinum and iridimn is ivory~ which has the thrther advantage of resisting moisture and other atmospheric influences, as is shown by cave tbssils. The standard weights should, therefore, be kept in glass cylinders, with ivory caps at top and bottom.--Comptes Rendu~. C.
15'ec(mtiorts in Comt)aring lVeigh~. [Jour. Frank. Inst.,
Irrigation by the T a g u s . - - A proposal has been laid before the Portuguese Government to build a dam across the river Tagus, about 20 kin. (12"43 miles) above A1)rantas, in order to raise the level sufficiently to irrigate about 400,000 trueus (988,657 acres) of the adjoining lands. The expense would be very small in colnl)arlson with the increased value of the land, which is estimated at 600,000,000 francs ($120,000,000), or nearly one-third of the Portuguese national debt. African l~ailway.--Dul)on('hel's 1)rqieeted railway tbr connecting Algeria with Soudan continues to excite" great interest in l?ranee. A commission of 65 members has been al)i~ointed , and divided into four sub-commissions. The first, under the presidency.of de Lesseps, is to collect statistical and eeonomlcal intbrmation; the second, under Duponehel, is devoted to technical studies and the determination of routes; the third is to have charge of the explorations, and the fourth will consider international questions, especially with reference to the Moors, the Tripolitans and the Toncuezs. Many of the senators and deputies, who are members of the commission, have visited Algeria in order to understand the different projects which arc to be brought before them.-- Les .Mondes. C. Precautions in Comparing Weights.--Deville and Mascart, in explaining the construction of' the international geodetic standard, give an interesting account of some of the necessary precautions: During the long series of operations upon which a comparison of two weights is based, a balance should never be opened. Its cage, composed of two envelopes of glass, bordered with cloth, should be guarded from the external air, which would change the hygrometric state of the interior, and which would introdnee dust. The particles of dust notch the knife-edges, and change the velvet linings of the weight-boxes into a material comparable to emery-paper. Air may be forced into the interior, at the rate of 4 or 5 litres (4"227 or 5"283 qts.) per hour, being first deprived of dust by filtration through cotton, and dried by chloride of potassium or other dessicatives. The substance which seems to produce the least wcar on alloys of platinum and iridimn is ivory~ which has the thrther advantage of resisting moisture and other atmospheric influences, as is shown by cave tbssils. The standard weights should, therefore, be kept in glass cylinders, with ivory caps at top and bottom.--Comptes Rendu~. C.