down to the 5.3 magnitude. It is to be remembered, in considering this data, that a star of say the second magnitude is only 1⁄2.5 as bright as a star of the first magnitude, i. e., one magnitude differs from another by the factor 2.5 in brightness. However the total radiation may be entirely different as may be noticed in Table I. In this table the last column gives the spectral classification used by astronomers. The blue stars have the classification B, A. These stars pass into the yellow gradation F, G, K, the latter being yellowish-red. The red stars are Class M and the deep red ones are Class N. Keeping in mind this classification, it may be noticed that the red star α Orionis emits about eight times as much total radiation as the blue star, β Orionis, which is much brighter to the eye. A similar example is the yellow star α Auriga (Capella) and the beautiful red star, α Tauri (Aldebaran), both of which stars are familiar objects. The latter is only about one-half as bright to the eye; and yet it emits the same amount of total radiation as does the brighter star. Comparing stars of the same photometric brightness the 5.3-magnitude stars Φ Pegasi and 19 Piscium are interesting examples because of their smallness, and because the latter is of a deep red color. The latter follows the general rule that the redder the star the greater the amount of total radiation received. The number of these very red stars is very small and they were not conveniently situated for observation. However from the observations on numerous stars of Class M as compared with blue and yellow stars of the same photometric magnitude, it is to be expected that these very red stars, Class N, will be found to have, as a general rule, the highest emissivity of all. Among all the data collected, on 105 stars, there are no exceptions to the general classification, viz., the redder the star the greater the amount of total radiation emitted. To some, of course, this information is not unexpected. However, if the reader will pause for a moment and consider that some of these measurements were made on starlight which left its source more than 160 years ago, and that stellar distances are so inconceivably great that another 160 years must elapse before the arrival of starlight which is being emitted at the present moment, it will be evident that every measurement has a value of far greater importance than merely confirming our expectations which are based upon our preconceived notions of what is occurring on a star and in passing through interstellar space.
The second method of studying the quality of the radiations of red and of blue stars, by means of the absorption cell of water, is more limited in range, because of the weakness of the radiations received. Only a few stars could therefore be investigated by this method. From the first method of observation it is to be expected that the total radiation from a red star contains more infra-red rays than does the total radiation from a blue star, and hence the amount transmitted by the
