Sidney Harry Jeffryes (20 July 1884 – 16 October 1942) was an early Australian wireless telegraphy operator. Trained by Australasian Wireless Co., Ltd., he was initially employed on coastal shipping and established at least one record for distance transmission. But he is best known for his service as the wireless officer at Cape Denison during the second year (February 1913 − December 1913) of the Australasian Antarctic Expedition under the command of explorer Douglas Mawson. His service ended in September 1913, two months prior to the relief of the shore party, when Jeffryes developed symptoms of paranoia and had to be relieved of his duties. Early life and family Jeffryes was born in Toowoomba, Queensland in 1884, second son of Henry Jeffryes and Helena (sometimes Ellen) Jeffryes née White. His father was a postmaster and telegraphist with the Queensland Post and Telegraph and following federation with the Postmaster-General's Department. Sidney's given name is indexed as Sydney in the records of the Queensland Registrar of BMD, but this may simply be a transcription error. His father Henry was a child of Henry Jeffryes and Sarah Jeffryes née Bland. After a long career with the Post Office, his father passed in 1910. His mother Helena was born in Essex in the UK and her father was William White. She died in 1932. There were at least seven children of the marriage: Louisa Ellen. Married Thomas Maxwell Gibb in 1898. Ivy Llalah (likely Lalla), born 1875. Married Walter Henry Donely in 1894. Ida Dorothea Maud, born 1879. Married Robert George Denny in 1904. Hulbert Trevannion, born 1881, died 1946. Teacher Gundiah (1910s). Married Isabel Jeffryes née King (died 1946) in 1906. Norma Fanny, born 1882. Sidney (alt Sydney) Harry, born 1884. Francis ("Frank') Edwin, born 1886. Died young in 1902 at Allora. Constance ("Connie") Eva, born 1888. Died 1949. Achieved unwanted prominence in an inheritance dispute. The family grew up in Allora. His father Henry spent almost 20 years in the district from 1889. He was initially assistant in charge of the local post office, but in September 1899 was appointed officer in charge. The death due to pneumonia of Sidney's younger brother Frank in July 1902 was a major tragedy for the family. A marble mural tablet to Frank's life was unveiled at the Allora State School in December 1902. Sidney's father was transferred to the Emerald Post Office in April 1909,