1. West-Germanic lengthening of consonants (the so called gemination of consonants).
There are languages in which the length of consonants has phonetic value (e.g. Swedish, Hungarian). Short (or single) consonants except rwere lengthened (or doubled) if followed by j or i and preceded by a short vowel. The resultened long consonant is called a geminate. [i],[j] sounds, which caused lengthening sometimes were preserved in the form of i or e or more often were lost.
Goth. bidjan – OE biddan; Germ. bitten
Goth. badi – OE bedd; Germ. bett
But in the final position long consonants were often shortened.
bedd → bed.
2. Rhotacism – the term comes from the Greek name of the letter r (rho). The consonant [z] resulting from the sound [s] by Verner’s Law, changed into[r] in the West and North Germanic languages.
s > z
r
Goth. laisjan (learn) – OE læ ran
Goth. maiza (more) – OE māra
This [r] was preserved in the middle of the word, but was lost in the final position in the West Germanic languages.
Goth. fisks – OE fisc – ON fiskr
Originally the old sound r and [r] developed from [z] were different in quality. That’s why in early runes two different symbols were used to designate these two sounds.
R = r1
= r2
In the textbooks the new sound r2 is often indicated as R and the old one as r.
e.g. fiskR