Trade centres at Ts'ingtao, a town within the bay.
This angle, therefore, divided by the magnifying power of the telescope gives the real angular distance of the centres of a double star.
To observe the position-angle of a double star it is only necessary to turn the position-web so that it shall be parallel to the line joining the centres of the components of the double star.
The distance between the centres of the two spectrographs shall be equal to the distance between the optical axes of the two viewing microscopes.
Pietro, forms a more or less protected basin, upon the shores of which are several small harbours (the most important being Carloforte), which are centres of the export of minerals and of the tunny fishery.