A study of galactic absorption as revealed by the reddenings of quasars.

1. This paper concerns quasars as a new means of studying galactic absorption.

2. It is argued that the residual δ(B-V)=B-V-(B-V)₀(z), where (B-V)₀(z) is the unreddened colour vs. redshift relation, is a promising indicator of galactic selective extinction for radio quasars with z <1.6. This is supported by evidence from δ(B-V) vs. M_V, δ(B-V) vs. A(Hubble counts), δ(U-V) vs. δ(B-V), and δ(B-V) vs. NHI diagrams.

3. The δ(B-V) vs. M_V diagram here introduced is consistent with the following propositions: a) R_V ≈ 3.3, b) there is a quasar population with a sharp cut-off in optical luminosities, and c) the redshifts are cosmological.

4. The δ(B-V) vs. A(Hubble counts) and δ(B-V) vs. NHI diagrams suggest that A_B, or the optical half-thickness of the Galaxy, is larger than 0^m.25. Revised K_V-corrections are derived for different values of A_B for z ≦ 2.0.

5. The δ(B-V) vs. NHI diagram reveals a remarkable two-branch structure, suggested to reflect high-latitude clouds towards the Local spiral arm. It is hypothesized that the clouds are mostly H₂.