He found the composition of varnishes an interesting subject, and as the best gums employed came from the tropics and were expensive he began to experiment with the exudations from American trees.

His employers hinted that he was wasting his time, but Harding continued, trying to test a theory that the texture and hardness of the gums might depend upon climatic temperature.

By chance, a resinous substance which had come from the far North fell into his hands, and he found that, when combined with an African gum, it gave astonishing results.

Before this happened, however, his employers had sent him out on the road; and as they were sceptical about his discovery and he would not take them fully into his confidence, they merely promised to keep his place open for a time.
Now he was going to search for the gum at his own expense.
"We'll order the outfit in the morning," he said presently, glancing toward a man who sat across the room.

"Do you think that fellow Clarke can hear?
I've a notion that he's been watching us." "Does it matter ?" "You must bear in mind that we have a valuable secret; and I understand that he lives somewhere in the country we are going through." As he spoke, the Hudson Bay agent came in and walked over to Clarke.
"That was good stuff you gave me a dose of last night," he said to him.
"It cured my ague right off." "It's a powerful drug," Clarke answered, "and must be used with discretion.