10 



DR. A. E. H TUTTON: 



the slate, however, does not touch the stone or concrete blocks anywhere, a clear air 

 space of an inch being left. The rest of the floor is concreted. and laid with a thick 

 layer of linoleum, which extends to within half an inch of the blocks all round. Hence 

 the stone supports for the two parts of the instrument are absolutely isolated, and in 

 risrid connection only with the foundations. 



O / 



As a precaution against the condensation of moisture on the solid stone walls they 

 were covered with asbestos, and afterwards matchboarded, leaving an air space of 



2 or 3 inches. 



The Thermostat. 



The temperature of the air of the room is controlled and maintained at the official 

 temperature, 62 F., entirely electrically, and for the sake of security by two different 

 independent methods, one involving the use of a mercury thermometer with platinum 

 contacts, and the other being a resistance-thermometer method. There are five 

 separate electric radiator heating lamps in symmetrical positions in the room, by which 

 all the artificial heating is accomplished ; four of these are controlled by whichever 

 thermostat is in use, the fifth remaining uncontrolled, as a reserve for use in the 

 depth of winter. 



The resistance method has the advantage of great sensibility owing to the size of 

 resistance-wire-grating adopted. A frame 7 feet 4 inches long by 8 inches high and 



3 inches wide holds 200 yards of stretched iron wire open-wound on porcelain 

 insulators. The current used is the 206-volts direct supply from the mains. The 

 zero is constant owing to the bifilar suspension of the galvanometer. Time lag is 

 exceedingly short, and the method adopted gives the average temperature of the 

 whole comparator. 



The mercurial thermometers are very large, there being ^-inch length of stem to 

 each degree. The platinum contacts are adjustable, and the whole arrangement has 

 the advantage of simplicity. 



If the temperature falls below G2, two radiator lamps are turned on by either the 

 mercurial or resistance-thermometer thermostat, whichever is in use at the time, the 

 turning on being effected through relays, a separate relay being provided for each 

 lamp. If the temperature rises above 62, the two lamps normally on are turned off. 

 The arrangements also provide for the automatic adjustment of the speed of an electric 

 fan. The relays and also the galvanometer have been specially constructed, and all 

 difficulty with regard to sparking has been overcome. 



Further details, together with drawings, will be communicated later concerning the 

 thermostats, after further experience has been obtained Math the various possible 

 methods of working them. 



The Interferometer. 



As regards the interferometer referred to under (1), the telescope and its supporting 

 pedestal and accessories are on the same model as that of the author's dilatometer and 



