Let us take the case in which the energy has to be borrowed from a steam engine. Supposing very small losses in the dynamo and piping, we may count upon a production of one cubic meter of hydrogen and 500 cubic decimeters of oxygen for 10 horse-power taken upon the main shaft, say an expenditure of 10 kilogrammes of coal or of about 25 centimes--a little more in Paris, and less in coal districts. If, consequently, we fix the price of the cubic meter of gas at 50 centimes, we shall preserve a sufficient margin. In localities where a natural motive power is at our disposal, this estimate will have to be greatly reduced. We may, therefore, expect to see hydrogen and oxygen take an important place in ordinary usages. From the standpoint alone of preservation of fuel, that is to say, of potential energy upon the earth, this new conquest of electricity is very pleasing. Waterfalls furnish utilizable energy in every locality, and, in the future, will perhaps console our great-grandchildren for the unsparing waste that we are making of coal.--_La Nature._ * * * * * [Continued from SUPPLEMENT, No. 818, page 13066.] MUSICAL INSTRUMENTS: THEIR CONSTRUCTION AND CAPABILITIES. By A.J. HIPKINS, F.S.A. LECTURE II. I will now invite your attention to the wind instruments, which, in Handel's time, were chiefly used to double in unison the parts of stringed instruments. Their modern independent use dates from Haydn; it was extended and perfected by Mozart, Beethoven, and Weber; and the extraordinary changes and improvements which have been effected during the present century have given wind instruments an importance that is hardly exceeded by that of the stringed, in the formation of the modern orchestra. The military band, as it now exists, is a creation of the present century. The so-called wood wind instruments are the flute, oboe, bassoon, and clarinet. It is as well to say at once that their particular qualities of tone do not absolutely depend upon the materials of which they are made. The form is the most important factor in determining the distinction of tone quality, so long as the sides of the tube are equally elastic, as has been submitted to proof by instruments made of various materials, including paper. I consider this has been sufficiently demonstrated by the independent experiments of Mr. Blaikley, of London, and Mr. Victor Mahillon, of Brussels. But we must still allow Mr. Richard Shepherd Rockstro's plea, clearly set forth in a recently published treatise on the flute, that the nature and the substance of the tube, by reciprocity of vibration, exercise some influence, although not so great as might have been expected, on the quality of the tone. But I consider this influence is already acknowledged in my reference to equality of elasticity in the sides of the tube.