142 POPULAR SCIENCE MONTHLY. 



This is illustrated by giving the differences as found, (1) by 

 Eowland, (2) by Guillaume, (3) by Wiebe, between a Kew ther- 

 uiometer and the air thermometer. It is clearly important to establish 

 in England a mercury scale of temperatures which shall be comparable 

 Avith the hydrogen scale, and it is desirable to determine as nearly as 

 may be the relation between this and the existing Kew scale. 



I am glad to say that in this endeavor we have secured the valuable 

 cooperation of Mr. Powell, of the Whitefriars works, and that the 

 first specimens of glass he has submitted to us bid fair to compare 

 well with the 16"'. Another branch of thermometry at which 

 there is much to do is the measurement of high temperature. 

 Professor Callendar has explained here the principles of the re- 

 sistance thermometer, due first to Sir W. Siemens. Sir W. C. Eoberts- 

 Austen has shown how the thermopile of Le Chatellier may be used for 

 the measurement of high temperatures. There is a great work left for 

 the man who can introduce these or similar instruments to the manu- 

 factory and the forge, or who can improve them in such a manner as 

 to render their uses more simple and more sure. Besides, at tempera- 

 tures much over 1000° C. the glaze on the porcelain tube of the pyrom- 

 eter gives way, the furnace gases get in to the wire and are absorbed and 

 the indications become untrustworthy. We hope it may be possible to 

 utilize the silica tubes shown here by Mr. Shenstone a short time since 

 in a manner which will help us to overcome some of these difficulties. 

 Here is another subject of investigation for which there is ample scope. 



So far we have discussed new work, but there is much to be done in 

 extending a class of work which has gone on quietly and without much 

 show for many years at the Kew Observatory. 



Thermometers and barometers, wind gauges and other meteorological 

 apparatus, watches and chronometers and many other instruments are 

 tested there in great numbers and the value of the work is undoubted. 

 The competition among the best makers for the first place, the best 

 watch of the year, is most striking and affords ample testimony to the 

 importance of the work. Work of this class we propose to extend. 



Thus there is no place where pressure gauges or steam indicators 

 can be tested. It is intended to take up this work, and for this purpose 

 a mercury pressure column is being erected. Bushy House from base- 

 ment to eaves is about 55 feet in height. We hope to have a column of 

 about 50 feet in height, giving a pressure of about 20 atmospheres; it 



