I. _The position of the stars_ is here generally given in galactic longitude (_l_) and latitude (_b_). Moreover their equatorial coordinates (α and δ) are given in an abridged notation (αδ), where the first four numbers give the right ascension in hours and minutes and the last two numbers give the declination in degrees, the latter being printed in italics if the declination is negative. Eventually the position is given in galactic squares, as defined in §2. II. _The apparent motion of the stars_ will be given in radial components (_W_) expressed in sir./st. and their motion perpendicular to the line of sight. These components will be expressed in one component (_u_0_) parallel to the galactic plane, and one component (_v_0_) perpendicular to it. If the distance (_r_) is known we are able to convert these components into components of the linear velocity perpendicular to the line of sight (_U_ and _V_). III. _The intensity of the light_ of the stars is expressed in magnitudes. We may distinguish between the _apparent_ magnitude (_m_) and the _absolute_ magnitude (_M_), the latter being equal to the value of the apparent magnitude supposing the star to be situated at a distance of one siriometer. The apparent magnitude may be either the _photographic_ magnitude (_m′_), obtained from a photographic plate, or the _visual_ magnitude (_m_) obtained with the eye. The difference between these magnitudes is called the _colour-index_ (_c_ = _m′_-_m_). IV. _The characteristics of the stellar radiation_ are the mean wave-length (λ_0) and the dispersion (σ) in the wave-length. _The mean wave-length_ may be either directly determined (perhaps as _effective_ wave-length) or found from the spectral type (spectral index) or from the colour-index. There are in all eight attributes of the stars which may be found from the observations:--the spherical position of the star (_l_, _b_), its distance (_r_), proper motion (_u_0_ and _v_0_), radial velocity (_W_), apparent magnitude (_m_ or _m′_), absolute magnitude (_M_), spectral type (_Sp_) or spectral index (_s_), and colour-index (_c_). Of these the colour-index, the spectral type, the absolute magnitude and also (to a certain degree) the radial velocity may be considered as independent of the place of the observer and may therefore be considered not as only apparent but also as _absolute_ attributes of the stars. Between three of these attributes (_m_, _M_ and _r_) a mathematical relation exists so that one of them is known as soon as the other two have been found from observations. FOOTNOTES: [Footnote 1: Meddelanden från Lunds Observatorium, No. 41.] [Footnote 2: Meddelanden från Lunds Astronomiska Observatorium, Serie II, No. 14.] [Footnote 3: Annals of the Harvard Observatory, vol. 50.]