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certain arc voltage and some projectionists who have volt meters adhere to the instructions and then write and ask why they cannot get results; and I may say that to always have the same arc voltage with a given amperage is an impractical thing to do in projection. What you can do in a laboratory where things are right, and what can be done in a projection room, where usually but few things are as they should be, are two very different propositions. You send out instructions to operate at, say 65 volts. The projectionist tries to do it and cannot get results ; perhaps his failure is due to lack of proper ventilation in the lamp house, perhaps to other things. Anyhow, it will not work. I have advised carbon manufacturers and others to be careful in sending out such instructions because it makes trouble.
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Mr. Campe: In that connection I might say that we know what operating conditions will give the best results, for instance, with higher amperage, higher arc voltage must be used. We try to give the operator some idea of how to obtain conditions which will give the best results. We do find under certain conditions that the way in which the lamp housing is ventilated will disturb conditions to a certain extent. What we are trying to do for the projectionist is to give him instructions which will serve as a guide in achieving the best results.
Mr. Richardson: That is all right, Mr. Campe, for you to put it that way, but many instructions have been sent out without any qualification at all. I have seen them myself . "Operate at 65 volts." The man tries to do it, and finds he cannot get results.
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