the weather forecast for london and the channel was "light airs, fine generally, milder." further down the fascinating column hackness read that "the conditions over europe generally favoured a continuance of the large anti-cyclonic area, the barometer steadily rising over western europe, sea smooth, readings being unusually high for this time of the year."

martin hackness, b.sc., london, thoughtfully read all this and more. the study of the meteorological reports was part of his religion almost. in the laboratory at the back of his sitting-room were all kinds of weird-looking instruments for measuring sunshine and wind pressure, the weight of atmosphere and the like. hackness trusted before long to be able to foretell a london fog with absolute accuracy, which, when you come to think of it, would be an exceedingly useful matter. in his queer way hackness described himself as a fog specialist. he hoped some day to prove himself a fog-disperser, which is another word for a great public benefactor.

the chance he was waiting for seemed to have come at last. november had set in, mild and dull and heavy. already there had been one or two of the dense fogs under which london periodically groans and does nothing to avert. hackness was clear-sighted enough to see a danger here that might some day prove a hideous national disaster. so far as he could ascertain from his observations and readings, london was in for another dense fog within the next four-and-twenty hours. unless he was greatly mistaken, the next fog was going to be a particularly thick one. he could see the yellow mists gathering in gower street, as he sat at his breakfast.

the door flew open and a man rushed in without even an apology. he was a little man, with sharp, clean-shaven features, an interrogative nose and assertive pince-nez. he was not unlike hackness, minus his calm ruminative manner. he fluttered a paper in his hand like a banner.

"it's come, hackness," he cried. "it was bound to come sometime. it's all here in a late edition of the telegraph. we must go and see it."

he flung himself into an armchair.

"do you remember," he said, "the day in the winter of 1898, the day that petroleum ship exploded? you and i were playing golf together on the westgate links."

hackness nodded eagerly.

"i shall never forget it, eldred," he said, "though i have forgotten the name of the ship. she was a big iron boat, and she caught fire about daybreak. of her captain and her crew not one fragment was ever found."

"it was perfectly still and the effect of that immense volume of dense black smoke was marvellous. do you recollect the scene at sunset? it was like looking at half-a-dozen alpine ranges piled one on the top of the other. the spectacle was not only grand, it was appalling, awful. do you happen to recollect what you said at the time?"

there was something in eldred's manner that roused hackness.

"perfectly well," he cried. "i pictured that awful canopy of sooty, fatty matter suddenly shut down over a great city by a fog. a fog would have beaten it down and spread it. we tried to imagine what might happen if that ship had been in the thames, say at greenwich."

"didn't you prophesy a big fog for to-day?"

"certainly i did. and a recent examination of my instruments merely confirms my opinion. why do you ask?"

"because early this morning a fire broke out in the great petroleum storage tanks, down the river. millions of gallons of oil are bound to burn themselves out—nothing short of a miracle can quench the fire, which will probably rage all through to-day and to-morrow. the fire-brigades are absolutely powerless—in the first place the heat is too awful to allow them to approach; in the second, water would only make things worse. it's one of the biggest blazes ever known. pray heaven, your fog doesn't settle down on the top of the smoke."

hackness turned away from his unfinished breakfast and struggled into an overcoat. there was a peril here that london little dreamt of. out in the yellow streets newsboys were yelling of the conflagration down the thames. people were talking of the disaster in a calm frame of mind between the discussion of closer personal matters.

"there's always the chance of a breeze springing up," hackness muttered. "if it does, well and good, if not—but come along. we'll train it from charing cross."

a little way down the river the mist curtain lifted. a round magnified sun looked down upon a dun earth. towards the south-east a great black column rose high in the sky. the column appeared to be absolutely motionless; it broadened from an inky base like a grotesque mushroom.

"fancy trying to breathe that," eldred muttered. "just think of the poison there. i wonder what that dense mass would weigh in tons. and it's been going on for five hours now. there's enough there to suffocate all london."

hackness made no reply. on the whole he was wishing himself well out of it. that pillar of smoke would rise for many more hours yet. at the same time here was his great opportunity. there were certain experiments that he desired to make and for which all things were ready.

they reached the scene of the catastrophe. within a radius of five hundred yards the heat was intense. nobody seemed to know the cause of the disaster beyond the general opinion that the oil gases had ignited. and nothing could be done. no engine could approach near enough to do any good. those mighty tanks and barrels filled with petroleum would have to burn themselves out.

the sheets of flame roared and sobbed. above the flames rose the column of thick black smoke, with just the suspicion of a slight stagger to the westward. the inky vapour spread overhead like a pall. if hackness's fog came now it meant a terrible disaster for london.

further out in the country, where the sun was actually shining, people watched that great cloud with fearsome admiration. from a few miles beyond the radius it looked as if all the ranges of the world had been piled atop of london. the fog was gradually spreading along the south of the thames, and away as far as barnet to the north.

there was something in the stillness and the gloom that london did not associate with ordinary fogs.

hackness turned away at length, conscious of his sketchy breakfast and the fact that he had been watching this thrilling spectacle for two hours.

"have you thought of a way out?" eldred asked. "what are you going to do?"

"lunch," hackness said curtly. "after that i propose to see to my arrangements in regent's park. i've got grimfern's aeroplane there, and a pretty theory about high explosives. the difficulty is to get the authorities to consent to the experiments. the police have absolutely forbidden experiments with high explosives, fired in the air above london. but perhaps i shall frighten them into it this time. nothing would please me better than to see a breeze spring up, and yet on the other hand——"

"then you are free to-night?" eldred asked.

"no, i'm not. oh, there will be plenty of time. i'm going with sir edgar grimfern, and his daughter to see irving, that is if it is possible for anyone to see irving to-night. i've got the chance of a lifetime at hand, but i wish that it was well over, eldred my boy. if you come round about midnight——"

"i'll be sure to," eldred said eagerly. "i'm going to be in this thing. and i want to know all about that explosive idea."