May 1 8, 1876] 



NATURE 



59 



the determination of three great natural "standards — of 

 length, time, and mass, and their combinations. 



Another branch of the general subject is the Measure- 

 ment of Light, which may be divided into two principal 

 sections, that including the measurement of the wave- 

 length of lights of different colours, and the angle of 

 polarization, which belongs purely and entirely to physical 

 science ; and the measurement of the intensity of light by 

 photometry, which, while involving also physical problems 

 of the highest order, has an important bearing also upon 

 applied science. The principal methods that have been 

 hitherto employed in photometry are by the comparison 

 of shadows, that of Rumford and Bouguer ; by employ- 

 ing a screen of paper with a grease- spot, the lights to be 

 compared being so adjusted that the spot does not differ 

 in appearance from the rest of the paper, Bunsen's 

 method ; Bister's, by determining in combustion the 

 amount of carbon contained in a given volume of a gas ; 

 and the one lately introduced by Prof. Adams and Dr. 

 Werner Siemens, by measuring the variation in the 

 electrical resistance of selenium, under varying intensities 

 of light. 



Before concluding, I wish to call your attention to two 

 measuring instruments which do not fall within the range 

 of any of the divisions before indicated. The first is an appa- 

 ratus designed chiefly by my brother. Dr. Werner Siemens, 

 by which astream composed of alcohol and water, mixed in 

 any proportion, is measured in such a manner that one train 

 of counter wheels records the volume of the mixed liquid ; 

 whilst a second counter gives a true record of the amount 

 of absolute alcohol contained in it. The principle upon 

 which this measuring apparatus acts may be shortly de- 

 scribed thus : — The volume of liquid is passed through a 

 revolving drum, divided into three compartments by radial 

 divisions, and not dissimilar in appearance to an ordinary 

 wet gas-meter ; the revolutions of this drum produce 

 the record of the total volume of passing liquid. The 

 liquid on its way to the measuring drum passes through 

 a receiver containing a float of thin metal filled with proof 

 spirit, which float is partially supported by means of a 

 carefully-adjusted spring, and its position determines that 

 of a lever, the angular position of which causes the alcohol 

 counter to rotate more or less for every revolution of the 

 measuring drum. Thus, if water only passes through the 

 apparatus the lever in question stands at its lowest posi- 

 tion, when the rotative motion of the drum will not be 

 communicated to the alcohol counter, but in proportion 

 as the lever ascends a greater proportion of the motion 

 of the drum will be communicated to the alcohol counter, 

 and this motion is rendered strictly proportionate to the 

 alcohol contained in the Uquid, allowance being made in 

 the instrument for the change of volume due to chemical 

 affinity between the two liquids. Several thousand in- 

 struments of this description are employed by the Russian 

 Government in controlling the production of spirits in 

 that empire, whereby a large staff of officials is saved, 

 and a perfectly just and technically unobjectionable 

 method is estabhshed for levying the excise dues. 



Another instrument, not belonging to any of the classes 

 enumerated, is one for measuring the depth of the sea 

 without a sounding line, which has recently been designed 

 by me, and described in a paper communicated to the 

 Royal Society. Advantage is taken in the construction 

 of this instrument, of certain variations in the total attrac- 

 tion of the earth, which must be attributable to a depth 

 of water intervening between the instrument and the solid 

 constituents of the earth. It can be proved mathemati- 

 cally that the total gravitation of the earth diminishes 

 proportionately with the depth of water, and that if an 

 instrument could be devised to indicate such minute 

 changes in the total attraction upon a scale, the equal 

 divisions on that scale would represent equal units of 

 depth. (See Nature, vol. xiii., p. 431.) 



Gravitation is represented in this instrument by a 



column of mercury resting upon a corrugated diaphragm 

 of thin steel plate, which in its turn is supported by the 

 elastic force of carefully tempered springs representing a 

 force independent of gravitation. Any change in the 

 force of gravitation must affect the position of this dia- 

 phragm and the upper level of the mercury, which causes 

 an air-bubble to travel in a convolute horizontal tube of 

 glass placed upon a graduated scale, the divisions of 

 which are made to signify fathoms of depth. Special 

 arrangements were necessary in order to make this in- 

 strument parai/iertnal, or independent of change of tem- 

 perature, as also independent of atmospheric density, 

 which need not be here described. Suffice it to say that 

 the instrument, which has been placed on board the S. S. 

 Faraday during several of her trips across the Atlantic, 

 has given evidence of a remarkable accordance in its 

 indications with measurements taken by means of Sir 

 William Thomson's excellent pianoforte wire-sounding 

 machine ; and we confidently expect that it will prove a 

 useful instrument for warning mariners of the approach 

 of danger, and for determining their position on seas, the 

 soundings of which are known. 



Another variety of this instrument is the horizontal 

 attraction meter, by which it will be possible to obtain 

 continuous records of the diurnal changes in the attrac- 

 tion of the sun and moon as influencing the tides. This 

 instrument belongs, however, rather to the domain of 

 physics than to that of mechanical science. 



These general remarks upon the subject of measure- 

 ment may suffice to call your attention to its importance, 

 several branches of whichj^those of Linear, Cubical, and 

 Electrical Measurement, will now be dealt with. 



The discussions which will follow these addresses will 

 be carried on under circumstances such as have never 

 before co-operated, namely, the presence of leading men 

 of science of all civilised nations, who will take part in 

 them, and the easy reference which can be had to the 

 most comprehensive collection of models of scientific 

 apparatus — both of modern and ancient— which has ever 

 been brought together. 



SCIENCE AT THE MANSION HOUSE 



FOR the first time probably in the history of this 

 country, science has been publicly acknowledged as 

 a great force or power in the kingdom, on a level with 

 literature and art. This, we think, is the legitimate con- 

 clusion to be drawn from the entertainment on Saturday 

 by the Lord Mayor at the Mansion House of so many 

 distinguished representatives of science, following hard as 

 it did upon the opening of the loan collection by her 

 Majesty the Queen. The company was numerous — 

 there were about 300 present — as well as distinguished, 

 and included several eminent foreign representatives of 

 science, who have come over to the opening of the loan 

 collection. The meeting was quite as successful as such 

 meetings usually are, and the speeches on the whole much 

 more sensible and appropriate. The following report of 

 the speeches we take from the Morning Post : — 



The Lord Mayor, in proposing the toast of the evening, 

 " The Representatives of Science," spoke very happily. 

 We were scarcely, he said, conscious of what we owed 

 to science. If the inventor of the first small crane 

 or lever for lifting water from a well were to come upon 

 the scene now-a-days he would have some difficulty in 

 persuading himself that it was the same world, and not 

 some kind of paradise very far in advance of the world 

 with which, in his day, that person was acquainted. 

 Science was one of the mightiest of all the intellectual 

 pursuits that man could follow. His Lordship said he 

 had an intense admiration for the representatives of 

 literature, but he could hardly express the feehngs with 

 which he regarded the men who laboured in the various 

 phases of science. What did we owe to it? and what 



