March 27, 1902] 



NA TURE 



489 



Messrs. Sir VV. G. Armstrong, Whitworth and Co., who 

 exhibited in addition Sir J.Whitworth's original measuring 

 machine. A Pratt and Whitney measuring machine has 

 not yet arrived. In an adjoining room, thanks to the 

 courtesy of .Sir F. J. S. Hopwood and Mr. Chaney, there 

 was an interesting exhibit from the Standards Depart- 

 ment of the Board of Trade. King Henry VI I. 's yard 

 and Queen Elizabeth's pints were shown in proximity to 

 our modern standards. 



The electrical rooms are three in number. One of 

 these, in the basement, has a constant-temperature 

 chamber attached, and here were the British Association 

 standards of resistance; the coil "Flat" made by 

 Matthiessen about 1S64 and used by the original British 

 Association Committee on Electrical Standards was 

 shown to visitors, as well as some modern standards. 



The main electrical laboratories, however, are far from 

 complete: one of these, which is to be used for the funda- 

 mental units and standards, was occupied as a tea-room. 

 In the other, Mr. Campbell had, in the ten days which had 

 been available, set up some secondary standards in their 

 permanent positions, while other apparatus was exhibited 

 on tables in the middle of the room. A few antiquated 

 scales of historical interest aroused some criticism. They 

 were merely placed on the tables with the other 

 apparatus to indicate that a galvanometer with some 

 proper arrangement of lamp and scale formed part of the 

 installation required. 



The fundamental standard of electromotive force will 

 be the Clark cell, while current will be measured by the 

 drop in volts over a known resistance ; but for secondary 

 standards a Kelvin multicellular voltmeter of somewhat 

 special construction, a set of Kelvin balances and some 

 Weston instruments will be employed. The voltmeter 

 is read on a long scale in the form of the arc of a circle 

 some two metres in radius. Between 60 and no or 120 

 volts the scale is a very open one, some 5 cm. correspond- 

 ing to one volt. Thus it is easy to read to the tenth of a 

 volt. For use with the instrument a special resistance box 

 containing ten coils has been wound by Mr. Campbell. 



The first coil of 10,000 ohms resistance is divided into 

 two parts. One of these has a resistance of 1500, the 

 other of 8500 ohms ; each of the others is 10,000 ohms. 

 Each coil is of manganin, wound in sections, which are ar- 

 ranged so as to be non-inductive, and each coil will stand 

 an E.M.F. of more than 100 volts. Thus 1000 volts may 

 safely be applied to the whole. A current can be passed 

 through the whole box and adjusted by means of external 

 resistances until the drop between the first and second 

 terminal just balances the E.M.F. of one Clark cell — 

 14,340 volts — in series. In this case the drop across each 

 coil after the first is 10 volts, and by connecting the 

 voltmeter in turn to the proper terminals of the box its 

 scale can be calibrated. When this has been done the 

 instrument is ready for reading directly potential 

 differences between 50 and 120 volts ; below 50 the 

 scale is too contracted. To measure voltages above 

 120 volts, the box is used ; the total volts are put on 

 between the end terminals ; the box enables these to be 

 subdivided to tenths, and a convenient number of tenths 

 can be measured directly on the voltmeter scale. 



In another corner of the room were the standard air 

 condensers of the British Association ; these, which 

 consist of a series of concentric cylinders, have been 

 ■described by .Mr. Glazebrook in some of the reports of 

 the Electrical Standards Committee ; on a table near by 

 was shown the apparatus for determining their capacity, 

 a Wheatstone's bridge box of platinum silver coils by 

 Elliott Bros, and a rotating commutator made by Pye 

 and Son, of Cambridge, the speed of which is controlled 

 by a stroboscopic arrangement viewed through dia- 

 phragms attached to a standard fork. 



It is intended at once to set about constructing from 

 these condensers standards of capacity for commercial use. 



NO. I 69 I, VOL. 65] 



On another table was set up in a convenient form the 

 apparatus for measuring by the ballistic method the per- 

 meability and hysteresis of an iron ring, while close by the 

 latest pattern of Ewing's permeameter was on exhibition. 



In the centre of the room were shown two resistance 

 boxes by Wolff, of Berlin ; one of these was a poten- 

 tiometer box with a wide range of applicability, the other 

 an ingenious modification of the Kelvin double bridge 

 which is used extensively at the Reichsanstalt for the 

 measurement of small resistances. 



The commercial testing of iron and steel or of measuring 

 apparatus, if undertaken on a large scale, will probably 

 be carried out ultimately in a room attached to the 

 engineering laboratory ; most of the arrangements which 

 have just been described are fitted rather for the con- 

 struction and verification of secondary standards than 

 for purely commercial testing. 



A fourth wing of the building contains the chemical 

 laboratory, which calls perhaps for no particular descrip- 

 tion ; it was described as workmanlike by a very capable 

 judge on the nineteenth, and that may suffice. .'V chemical 

 laboratory is essential, but it is not desirable that it 

 should be very elaborate. 



The laboratory contained a large collection of glass 

 vessels, flasks, burettes, &c., lent by Messrs. Gallenkamp ; 

 these were intended to illustrate one branch of the new 

 work, the standardisation of such apparatus for which 

 there seems a great opening. The vessels exhibited 

 bore the stamp of the Reichsanstalt. 



The system of electric wiring adopted requires a 

 special notice. There are two distinct sets of circuits ; 

 one of these, connected to the lamps and to numerous 

 plug points, is fed from the dynamo or the cells at a 

 steady voltage of lOD volts. It is used for lighting and 

 for the supply of power. 



For the experimental work there is a separate bittery 

 of 55 cells. These are arranged in groups of 5, the first 

 group being further subdivided ; the positive poles of the 

 cells are connected to a series of horizontal brass bars at 

 the back of the main switchboard : the negative poles are 

 connected to a series of isolated blocks, which, by means 

 of switches on the front of the board, can be put into 

 contact with the corresponding horizontal bars ; the 

 positive pole of each group is one bar lower than the 

 negative pole of the same group. Thus if the switches 

 are all closed the cells are in series ; the top horizontal 

 bar is negative, and there is a constant rise of 10 volts 

 between each two consecutive bars. On the front of the 

 bjard are a series of vertical bars, and from the tops of 

 these the experimental circuits, of which there are thirty, 

 lead away through fuses. These vertical bars can be 

 plugged through to the horizontal bars at the back, and 

 thus a series of voltages rising by steps of 10 volts can 

 be distributed through the building. 



The normal discharge rate of the cells is 50 amperes, 

 but to obtain higher rates the cells can be connected in 

 groups of five in parallel. To do this with all the groups, 

 all the switches are opened ; two specially heavy vertical 

 bars are then connected by plugs, the one to all the 

 positive poles, the other to all the negative poles of the 

 battery. From these bars two circuits capable of taking 

 500 amperes lead away. 



The switchboard, which is a modification of that at 

 the Owens College Laboratory, was designed by Mr. 

 G. A. Steinthal, of Bradford, in accordance with the 

 suggestions of the director. Mr. Steinthal has carried 

 out all the experimental wiring. The distributing wires 

 are for the most part bare copper, and are carried on 

 porcelain insulators. Some of these wires go directly 

 to the various rooms, and are so arranged that it is 

 possible in any room to obtain simultaneously at least 

 two different voltages. Others of the distributing 

 wires go to three subboards arranged in a similar 

 manner to the miin board ; four circuits from the main 



