He worked with the astrophysics staff, measuring the radial velocity of stars and determining the orbits of spectroscopic binaries.

(The latter are binary star systems that could not be resolved with a telescope, but their orbital motions could be studied due to the doppler effect on their spectrum.)

In 1913, the government approved the project and Dr. Harper was sent to make measurements of the observing conditions at various sites.

He was also a member of the Royal Astronomical Society of Canada, being awarded their gold medal, then becoming a Fellow in 1913.

By 1938 he was suffering from ill-health, which was further undermined by a bout of pneumonia while representing Canada at the General Assembly of the International Astronomical Union in Stockholm.