586,312. Detectors. STANDARD TELEPHONES & CABLES, Ltd., SMYTH, C. N., and ROGERS, D. C. Jan. 20, 1944, No. 1155. [Class 40 (v)] [Also in Group XXXVI] Thermal devices for measuring or indicating the energy of electric waves set up in hollow resonators, wave guides, or coaxial lines comprise an envelope of glass or other fusible material sealed to and closed by a metal portion, a thermally-sensitive element being housed within the envelope and connected in series with leads which function as a loop aerial. As shown in Fig. 4, the envelope 40 is sealed to an annular metal plate 41 which is welded to a metal disc 51. The thermal device 46, which may be a thermo-junction, a fine resistance wire, or a directly-heated thermistor, is spot welded to electrodes 42, 44, one of which is secured at 43 to the plate 51 and the other passes out through a glass bead 45. A suitable D.C. measuring or indicating instrument is connected between the outer end of the electrode 44 and the plate 51. The envelope 40 is thrust into a hole in the wave guide &c. and the plate 52 closes the gap. Currents induced in the parts 42, 44, 46 operating as a loop pick-up affect the thermal device and give a reading on the external instrument. The latter, is shunted by a condenser which may comprise a plate 47 separated from the plate 51 by an insulating layer 48, and making contact by a spring wire 50 with the electrode 44. In another form of the invention, Fig. 2, a downward extension of the glass envelope is sealed to the underside of the metal plate 10 and the electrode 23 is secured to a member 17 which extends downwards through an aperture in the plate 10 and is sealed through the lower end of the envelope. The shunting condenser is formed by the member 17 separated by flat insulating layers 19 from two segmental members 15, 16 which fit closely within a cylinder 14 secured to the plate 10. The other electrode 20 is welded to the cylinder 14.