CHAPTER XVIII
A NEW THEORY
"Those robbers probably came in a light, rubber-tired rig, left itsomewhere around the corner, got into the bank, did the job and droveaway again," was the opinion of Mr. Thompson, as he crawled out of theroof scuttle, followed by the boys.
"But how did they get to the roof?" asked Ned. "You've got to explainthat."
"Easy enough," spoke the policeman. "You see this bank is in a row,with several other buildings, all about the same height. They couldhave climbed up the fire escapes, or they could have used a ladder.I'm inclined to the latter theory myself, for the fire escapes are onthe front of the buildings, and if they went up them they'd be seen,whereas they could put a ladder up in back."
The boys looked about them, and Bob took a couple of snap shots,including one of his two chums and the officer as they stood near theopened scuttle. As Mr. Thompson had said there was not much to see.The roof was a long one, extending over several buildings, and beingflat, and covered with a composition of tar and gravel, alternatingwith tin on some of the structures, made quite a place to stroll about.
Jerry walked a little away from Ned and Bob, who were listening toMr. Thompson's explanation of how Detective Blake had discovered thefinger marks in the dust around the scuttle rim, and had thus made hisdiscovery.
"Blake thinks the scuttle was left unhooked, or else that the thievesreached in with a bent wire, and lifted the hook from the catch," saidthe policeman.
The tall lad was walking over a stretch of tin roof, on a buildingtwo or three doors from the looted bank. There had been rain two daysprevious, followed by a brisk wind, which dried out the dust, andthere was now quite a coating of the latter on the tin. There was alsosomething else, and as Jerry caught sight of several marks in thedirt-coating he uttered an exclamation.
"Somebody with rubber-soled tennis shoes has been walking up here," hesaid.
He bent closer over the footprints, and then he saw another mark thatcaused him to spring up quickly, and call to his companions and thepoliceman.
"Look here!" he cried, beckoning to them.
"What's the matter?" demanded Ned, coming up on the run.
"Easy! Easy!" cautioned Jerry. "Don't trample on these marks. Look! Ifsome one hasn't been up here on a bicycle I miss my guess!"
"A bicycle!" exclaimed Bob. "Do you mean to say that the robbers rode abicycle up here?"
"There are the marks of the rubber tires plain enough," replied Jerry,pointing to them.
"That's no bicycle track!" declared Ned.
"Why not?" the tall lad wanted to know.
"Or, if it is, the fellow rode on one wheel, or else is more expertthan anyone I ever saw. See, there's only one straight mark, and thebest rider in the world turns his front wheel every now and then,making a separate track from the rear one. That's no bicycle mark."
"What is it then?" demanded Jerry. "Did some one roll a single bicyclewheel about on the roof for fun?"
Before Ned could reply, Bob, who had gone off several paces to theleft, uttered a cry.
"Here's another!" he shouted, pointing to the dusty tin roof. Hiscompanions hastened over, taking care to keep off the tracks, andthere saw another mark, exactly like the first.
For a moment Jerry Hopkins stared at the second impression. Then hewent back to look at the first one. Next he hurried forward and beganlooking at a space about midway between the two tire tracks. Hiscompanions and the policeman watched him curiously. Suddenly Jerrythrew up his hand as a signal.
"I've found it!" he cried.
"What?" asked Ned.
"The third track!" was the response. "Fellows it was no bicycle uphere. It was----"
"An aeroplane!" fairly burst out Ned and Bob together, for now, withthe discovery of the third impression, midway between and ahead ofthe first two, it was very plain to anyone who had had to do withaeroplanes that they were the marks of the three landing, or startingwheels, of such a craft, that had left the marks in the dust of theroof.
"An airship!" exclaimed the policeman. "Do you boys mean to say that anairship has been up here?"
"It certainly has," declared Jerry firmly. "Look here! There are moremarks farther on." He pointed just beyond a blank space, where thetin roof was clean of dust, and the marks were again visible in thesoft tar of another roof. "They landed here and made a start from here.They could easily do it. In fact this long, flat roof with the tarand gravel to give good traction, is an ideal starting place for anaeroplane."
"An aeroplane on the roof!" murmured the officer, as if unable tobelieve it. "Do you think, Jerry----"
"I think," interrupted the tall lad, "that the bank burglars camethrough the air, made a landing here unseen by anyone in the street,went down the scuttle, looted the safe, and made a flying start fromthis roof."
"Wait! Wait!" begged Mr. Thompson. "This is a new theory--I never heardthe like before. It needs a regular detective to consider this. Waituntil I get Blake up here. I'll wager it'll be news to him. Wait herefor me."
He hurried down the scuttle, and the boys eagerly looked for moreimpressions and talked about Jerry's discovery. They went to the end ofthe row of buildings, and there, where the roof was of tar and gravel,they found in the soft black material the plain impression of the threewheels. They came to a sudden stop before "the jumping-off place," asJerry called it, was reached.
"Here's where they sailed into the air," he declared confidently.
"Let's see if we can find where they landed," suggested Ned.
They did, at the opposite end of the row of roofs, just where a tallbuilding reared itself several stories higher than the row of lowstructures.
"They came down here all right," declared Jerry excitedly pointing tothe deep impression made by the wheels. The boys even found the placewhere the drag-brake had scraped a long line in the gravel, and that,to them, made their "case complete."
Suddenly the merchant's son uttered a cry, and straightened up.
"What's the matter?" asked Jerry in surprise.
"Those wheel marks!" gasped Ned. "Look! Those are new tires, Jerry. Notworn a bit, and they're the anti-skid style--see the corrugations andthe rubber-protruding cleats."
"I see 'em--what of it?"
"Don't you remember--Noddy Nixon's aeroplane--after he put on the newwheels, following his smash-up? Don't you remember? He had wheels justlike these--exactly like them. Look!"
Jerry glanced at his chum with wide-opened eyes. Then he looked down atthe marks. The light of remembrance came into his eyes.
"By Jove, Ned, you're right!" he exclaimed. "Noddy Nixon and BillBerry--and that talk I overheard between them--Noddy Nixon--hisaeroplane--I----"
At that moment Detective Blake, followed by President Carter of thelooted bank, and several of the directors, came out on the roof.