Fig. 28.
2. I have before me the vacuum tube shown by [Fig. 28], in which the dotted lines relate to details of manipulation only.
It is usually possible to detect the parts of which a piece of apparatus has been built up, for even the best-made joints exhibit evidence of their existence. Thus, although I did not make the tube that is before me, and cannot therefore pretend to say precisely in what order its parts were made and put together, the evidence which it exhibits of joints at the dotted lines A, B, C, D, E, F, enables me to give a general idea of the processes employed in its construction, and to explain how a similar tube might be constructed. I should advise proceeding as follows:—
Join a piece of tube somewhat larger than M to its end A, draw out the other end of the larger tube, and blow a bulb L as directed on [p. 47]. Then seal the electrode R into the bulb L ([p. 55]).
Blow a similar but larger bulb N from a large piece of tube sealed between two tubes of similar size to M, as described at [p. 50]. Cut off one of the tubes at B, and join the bulb N to M at B. Form the bulb Q in the same manner as in the case of L, seal into it the electrode R, and add the tube marked by the dotted lines at F.
Seal a narrow tube P to the end of a larger tube, and blow out the tube at the joint till the glass is thin and regular. Take a tube O, of similar size to M, slightly longer than P, contract its mouth slightly to meet the wide end of P at D, and after loosely supporting P inside O with a cork, or otherwise, close the end N of O by sealing or corking it, and join P to O at D. Cut off O just above D at E, and join it to the bulb Q, closing either O or F for the purpose. Cut off the end of O at C parallel to the end of P, and connect O to N, using F for blowing the joint at C. F may be used subsequently for introducing any gas into the tube, and, when a vacuum has been established, may be sealed before the blow-pipe.
