454 Messrs. Threlfall and Pollock on some 



very small wave-length or having longitudinal com- 

 ponents. This is probably a special case of (4) — at 

 least if we are to look to the tether to explain electricity 

 and magnetism dynamically. 

 6. The radiation is a phenomenon of a new order entirely 

 unconnected in any way with anything in our past 

 experience. 



Source of Radiation. 



Being thrown entirely on our own resources for means of 

 production of the radiation — all the Crookes's tubes in our 

 possession being almost useless — we arrived at the form of tube 

 shown in fig. 1. These tubes are easily made ; the surface 



Fig. 1. 



opposite to the kathode being spherical, can be made very 

 thin, and the electrodes are kept well apart. The kathode 

 is best made very nearly plane — if concave it will easily fuse 

 the thin glass against which its rays are projected ; we have 

 lost many tubes from this cause. We have found that the 

 bulb may be conveniently about three or four centimetres in 

 diameter and the main tube as little as 1*5 to 2 cm. in diameter. 

 The expansions round the electrodes are intended to obviate 

 local heating, for it is not always easy to prevent oscillatory 

 discharges and consequent *' kathoding " from the " anode/'' 

 The chief merits from our point of view T , however, were that 

 tie tubes were very easy to make out of comparatively small 

 glass tubing. Their volume is small, so that they can be 

 exhausted quickly, and they give very intense action. In 

 fact one tube — the bulb of which ultimately fused under the 



