Acting no doubt upon this expressed belief, Audubon became a subscriber to Gould's _Century of Birds_, published in 1831, and also to his _Birds of Europe_ (1832-37). In the preface to the latter work, "J. J. Audubon, Esq.," and twenty others are thanked "for the warm interest which they have at all times taken in the present work"; it was also said that the greater part of the plates of this series, those of his _Century of Birds from the Himalaya Mountains_ and his _Monograph on the Trogons_, as well as three-quarters of those of the _Monograph on the Toucans_, "have been drawn and lithographed by Mrs. Gould, from sketches and designs by myself always taken from nature." It should be noticed also that Gould appeared as a subscriber to _The Birds of America_ in 1838, but his name was soon dropped. Gould was preëminently a museum naturalist, of strong commercial instincts, and spent but little time in the field. His books were mainly composed of illustrations made by artists from stuffed specimens, with a text of so thin a quality as to possess little scientific value; but, as Alfred Newton has remarked, a scientific character was so adroitly assumed that scientific men have often been deceived. In his best work, that on the Humming Birds,[116] the plates are enlivened by numerous specimens of tropical flowers and fruits, an accessory not so noticeable in his early productions. It has been said that Gould sought and received Audubon's aid in the composition of some of his plates, and that thereafter his figures began to show more vitality. The over-zealous writer quoted above[117] made the charge that Gould not only received much unacknowledged aid from Audubon, but copied his drawings; he mentioned five cases of what he called "picking and stealing," in one of which the Red-headed Pochard is declared to have been copied from Audubon's Scaup Duck: "here the trick is so shallow," he adds, "that detection cannot for a moment be at fault. You see that the Scaup Ducks have been accurately outlined, then lifted from the original 'grounding,' and let down upon a new one, by Gould, who found it safer for his pencil to adjust earth and water differently beneath them, than to tamper in the slightest degree with the proportions of the figures themselves." Suffice it to say that there is little or no substantial basis for such odious charges.