The ratios between adenine and thymine and guanine and cytosine are constant and equal for a double stranded DNA. This proposition was made by?

Chargaff's rule applies only to ds DNA. The amount of adenine (A) is equal to that of thymine(T) and the amount of guanine(G) is equal to that of cytosine(C).

$\mathrm{A}=\mathrm{T},\mathrm{G}\equiv \mathrm{C}$