IN reply to Mr. Walter Chamberlain's inquiry (p, 198), it must be borne in mind that spark length is not per se a criterion of the energy delivered to a vacuum tube. The length of spark is more or ...

I SHALL be much obliged if any of your readers who work with the X-rays will give me their experience with the 10-inch coils. I have one by Apps, which is excellent in every way; but whether I take ...