Key points are not available for this paper at this time.
The previous theory by the author and Nagamiya (1951) is improved in this paper by introducing the shearing elastic constant c 44 , which is estimated by a procedure similar to that employed by Brennan. This shearing elastic constant couples the two types of vibrations, those normal to the hexagonal layers and those parallel. The theory shows that below 10°K the deviation from T 2 law becomes appreciable and the range of transition from T 2 to T 3 laws appears at a few degrees absolute. The calculated values agree with the experimental ones over the whole temperature range below 60°K Comments are given on recent other theories.
Kozo Komatsu (1955) studied this question.