Henrietta Swan Leavitt’s actual 1912 paper wherein she notes the pattern in cepheid variable stars. This finding would go on to have enormous impact and change the face of modern astronomy leading to Edwin Hubble’s universe expanding work. 

Her superior, Edward Pickering, led the department in which Leavitt worked. This is his summation of her incredible findings, which she published in the  Annals of Harvard College Observatory in 1908 (see here).