Robison could learn no more of the new contrivance from Watt at that time; but on the same evening he accidentally met a mutual acquaintance, who, supposing he knew as usual the progress of Watt’s experiments, observed to him, “Well, have you seen Jamie Watt?” “Yes.” “He’ll be in fine spirits now with his engine?” “Yes,” said Robison, “very fine spirits.” “Gad!” said the other, “the separate condenser’s the thing: keep it but cold enough, and you may have a perfect vacuum, whatever be the heat of the cylinder.” This was Watt’s secret, and the nature of the contrivance was clear to Robison at once. [Illustration: DR. JOSEPH BLACK.] It will be observed that Watt had not made a secret of it to his other friends. Indeed Robison himself admitted that one of Watt’s greatest delights was to communicate the results of his experiments to others, and set them upon the same road to knowledge with himself; and that no one could display less of the small jealousy of the tradesman than he did. To his intimate friend, Dr. Black, he communicated the progress made by him at every stage; and the Doctor kindly encouraged him in his struggles, cheered him in his encounter with difficulty, and, what was of still more practical value at the time, he helped him with money to enable him to prosecute his invention. Communicative though Watt was disposed to be, he learnt reticence when he found himself exposed to the depredations of the smaller fry of inventors. Robison says that had he lived in Birmingham or London at the time, the probability is that some one or other of the numerous harpies who live by sucking other people’s brains, would have secured patents for his more important inventions, and thereby deprived him of the benefits of his skill, science, and labour. As yet, however, there were but few mechanics in Glasgow capable of understanding or appreciating the steam-engine; and the intimate friends to whom he freely spoke of his discovery were too honourable-minded to take advantage of his confidence. Shortly after, Watt fully communicated to Robison the different stages of his invention, and the results at which he had arrived, much to the delight of his friend.