Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. T the time of his death in 1901 Professor P. G. Tait had just finished editing the Second Volume of his Collected Scientific Papers. The series is now completed by this Memorial Volume whose preparation I undertook at the request of Mrs Tait, who kindly placed a great deal of material at my disposal, and who, together with the other members of the family, has been closely in touch with the work as it proceeded.