George Fiusdale Jowett was born in Bradford, Yorkshire but he emigrated to Canada in 1910. He was instrumental in the formation of the American Continental Weightlifting Association and was a renowned strength athlete in his own right. He was also well known as an author and magazine editor (though known to be prone to exaggeration so much of his writing, particularly in regards to strength feats is general thought to be taken with a pinch of salt).
This pamphlet, published in the UK (note the Moulding, rather than Molding of the original series) is a compilation of extracts from the Molding Mighty Muscles series by George F Jowett. Unfortunately it is undated though I suspect this is mid 20th century.