In the last four days I have got the spectrum given by Tantalum, Chromium, Manganese, Iron, Nickel, Cobalt, and Copper and part of the Silver spectrum. The chief result is that all the elements give the same kind of spectrum, the result for any metal being quite easy to guess from the results for the others. This shows that the insides of all the atoms are very much alike, and from these results it will be possible to find out something of what the insides are made up of.