Durability of cement drain tile and concrete in alkali soils; third progress report (1919–1920)

✍ Scribed by G.M. Williams

• Publisher: Elsevier Science
• Year: 1922
• Tongue: English
• Weight: 195 KB
• Volume: 194
• Category: Article
• ISSN: 0016-0032
• DOI: 10.1016/s0016-0032(22)90064-x

✦ Synopsis

field, partial achromatism) over the usual types of quartz spectrographs for investigating the shorter waves.

III. '4 Stigmatic Concazv

Gvatirlg ,Ilozt&zg.-The Wadsworth mounting in which the slit is, in effect, placed at infinity with the aid of an auxiliary mirror, thus filling the concave grating with parallel light, gives spectral images which are practically free from astigmatism.

This permits the use of diaphragms in front of the slit for the photography of comparison spectra in juxtaposition, and makes it possible to study the spectra of interferences. or of localized parts of sources whose images are focussed on the slit. Compared with the Rowland type of mounting, it requires only about one-fourth the space, and although the dispersion is reduced to about half, the intensities of the spectra are increased more than four-fold.

The characteristics are outlined and detailed drawings of the apparatus are reproduced.

IV. The Preparation of Spectrum