it was not a large island, as islands go, being something less than half a mile in extent by a quarter of that in breadth. but it was densely wooded, and the underbrush was so thick as to make exploration difficult. nevertheless, after securing the raft to the trunks of trees by means of stout creepers twisted and used as ropes, the boys pushed exploration of the island in order to determine whether there was some means of reaching the mainland from it.

that, however, would be difficult. at no place did either river bank approach the island closely. the likeliest chance appeared to be to cross to the left bank, that upon which was the main party, by means of a score of half-submerged rocks, between and over which the water boiled and foamed. these rocks lay between the forward end of the island and the shore.

“we might be able to leap from rock to rock in some cases, and in others to bridge the chasms with poles,” said jack, considering the situation, as he and the two others, with matse behind them, stood on the shore near these rocks.

“but then,” said frank, “we’d have to abandon the raft.”

jack nodded gloomily.

at one other point, another solution suggested itself. near the upstream end of the island, on the side opposite that upon which they had landed, the mainland was less than one hundred yards away. and through this lesser channel the water, as they ascertained by tossing chips into the current, flowed less swiftly. a strong swimmer, heading upstream, probably would be able to make his way to the opposite shore before being swept down into the rapids below. he could carry a rope and, once such a connection was made, other ropes could be passed back and forth until a strong enough ferry was established to make it possible to transport the raft without danger of the ropes parting and letting it be carried down.

but where was rope to be obtained? examination of the boxes revealed numbers were bound with short ends of rope. but all these tied together would not be of sufficient length to bridge the channel even once. and more than one rope, as experience had revealed, would be necessary to ensure safety.

“we might make a rope of creepers,” bob suggested, at length, as, after a survey of their resources, the three stood on the raft, gazing wryly at each other.

“dad has several big coils of rope with him,” said jack. “if we could only get in touch with him and tell him to cross the river up above and come down on the right bank.”

bob looked at his watch. “more than three hours since we started our runaway journey,” he commented. “great scott, i hadn’t realized how long we’d been on the way. why, we must have been carried fifteen miles downstream.”

“all of that,” said jack. “and dad will have a hard time making his way through the underbrush and jungle growth along that marshy river bank on his side of the stream. he’ll keep hunting till he finds us. but we can hardly look for him to put in an appearance today. well, thank goodness, we not only saved ourselves but the raft and its supplies, too. that’s something. and we’ll find a way out of this all right.”

frank who, although the smallest of the three suffered most from the heat oppression, had remained silent, sitting on a box and fanning his flushed face with his sun helmet. now he leaped to his feet, and his eyes lost the drowsy look induced by the heat and sparkled with animation.

“jack, if we’ve been gone more than three hours, it’s dollars to doughnuts that we can get in touch with your father.”

“you mean—”

“radio. no less,” answered frank, triumphantly. then he proceeded to elaborate.

“your father, as you say, cannot have pushed his way very far through that jungle growth in three short hours. he knows that whether the blacks swam for it or not, we would stick to the raft as long as there remained a chance to save it. so he will figure either that we have reached shore somewhere below him with the raft or else that we are still being carried downstream. after he has forced his way through the jungle a mile or two, what is he most likely to do? why, to set up the radio and start calling for us on the chance that we are doing likewise. doesn’t that seem probable.”

“probable or not,” said bob, beginning at once to poke about amongst the contents of the raft in search of the box containing the spare transmitting set; “at least putting up the radio will give us something to do.”

“right,” said jack, laying his hand on a case, “and here it is. now to get it set up.”

the blacks, with the exception of matse who sat dozing on the bank, were not in sight, having retired to a glade back amongst the trees and gone to sleep. their philosophy seemed to be to leave worry to the young white men.

“anyhow, we wouldn’t need them,” decided jack. “because we won’t have to take this stuff ashore to set it up. we can put it up right here on the raft. water is a fine conductor and will give us a good ground. and we can have better luck out here in the open with our aerial than in amongst the trees.”

with this the others agreed, and all went to work unpacking the apparatus. little was said as they worked, and so expert were they at this job of putting up a set in double-quick time in the wilds that in a very short space the loop aerial was in place, all the wires were connected, and then jack sat down at the instrument and began tuning in to the wave length his father would be employing.

at first there was no response, try as he would. and jack feared that perhaps water had penetrated the packing boxes and saturated some of the wiring. he put off the headpiece, and the three boys went over every inch of wire. true enough, what jack feared had really occurred. but only one small wire was wet. armature windings and other portions of the apparatus which could not have been dried out readily had they become saturated, had escaped.

“i suppose now we’ll have to build a fire and dry this out,” said jack, detaching the three foot strand of insulated wire connecting one post of the tuning coil with one of the end posts of the switch. “it’s a nuisance, but i can’t find any replacement wire.”

“no use building a fire,” said frank. “this sun is hot enough, goodness knows. that strand ought to dry out soon enough. let’s put it here,” he added, indicating a packing case standing in the sun from the surface of which heat waves visibly radiated.

that was done and then the boys sought the shaded end of the raft where they crouched, talking intermittently, while awaiting the result of the drying-out process. several times one or other went and turned over the wire and at length jack triumphantly declared it thoroughly dry. then the connection was restored, and again he put on the headpiece and tuned in.

bob and frank looked on anxiously. almost at once a broad grin broke over jack’s face.

“it’s dad,” he cried; “calling for us.”

then pulling the transmitter toward him, he began to reply. this two-way set for both transmitting and receiving was of the boys’ own design. simpler, more compact, than any device turned out by the great companies manufacturing radio supplies, it had served them well in other lands and climes and in the most perilous of circumstances had proven their staunchest support. the impact of the voice against a sensitive diaphragm acted to automatically close the receiver. it was this which constituted the chief feature of the device, making the jump from transmission to reception and vice versa a matter of no account at all.

bob and frank, unable to hear what mr. hampton had to say, but listening to jack’s remarks, gathered the drift of the conversation. as frank had surmised, the main party had been so delayed in pushing down river through the jungle growth along the bank that only a couple of miles had been made. then, finding no trace of the runaway raft, mr. hampton had returned to their old camp site and obtained the radio which had not been set up for some days. rigging it up with niellsen’s aid, he had at once begun calling. when no reply was received, he had continued to call at fifteen-minute intervals. and it was one of these calls which had caught jack’s ear.

jack was outlining their situation on the island to his father. and after having heard how matters stood, the latter apparently, so far as bob and frank could gather from jack’s replies, was of their opinion regarding a method of rescue. consequently, he intended again to essay the crossing of the river at the old camp site, after which he would make his way down the right bank which was higher ground and freer of jungle growth to the point opposite the island where the boys believed a swimmer could cross the channel with a rope.

finally, jack closed communication and turned to his comrades. relief at this quick opening of communication with the main party was uppermost in the minds of all. once more they had reason to be thankful that radio was at their command.

“and a mighty good thing, too,” said jack, “that we took frank’s advice, and split our equipment, so that both dad and ourselves are supplied.”

the attempt at rescue, however, could not be made until the following morning. the better part of the day already was sped. mr. hampton would spend the balance in crossing the river and starting downstream. he might, of course, reach a position opposite them before nightfall, as four hours of daylight yet were left. but the crossing could not be attempted except in daylight and so he would have to wait until the following day.

at length, after turning the matter over and considering it from all angles, the boys decided to go ashore and prepare some food. they had not eaten since their early morning breakfast. matse, accordingly, was aroused and sent to stir up the bearers. a case of tinned foods was opened, and the boys tossed materials for a meal to the bearers on shore.