Variable stars are of particular interest to astronomers because the light from them pulsates regularly, flaring and dying as though fuel were replenished at regular intervals. The rate of this pulsation has been found to be a measure to the candle power of the star. Its distance then can be determined by contrasting its actual candle power with the apparent magnitude as seen from the earth. [Illustration: _"Oh my God!" gasped Bell. He'd known this man before. A Secret Service man--one of the seven who had vanished._] Murder Madness PART THREE OF A FOUR-PART NOVEL _By Murray Leinster_ Seven United States Secret Service men have disappeared in South America. Another is found--a screaming homicidal maniac. It is rumored that they are victims of a diabolical poison which produces "murder madness." [Sidenote: More and more South Americans are stricken with the horrible "murder madness" that lies in The Master's fearful poison. And Bell is their one last hope as he fights to stem the swiftly rising tide of a continent's utter enslavement.] Charley Bell of the "Trade"--a secret service organization which does not officially exist--discovers that a sinister system of slavery is flourishing in South America, headed by a mysterious man known only as The Master. This slavery is accomplished by means of a poison which causes its victims to experience a horrible writhing of the hands, followed by a madness to do murder, two weeks after it is taken. The victims get relief only with an antidote supplied through Ribiera, The Master's Chief Deputy; but in the antidote there is more of the poison, which again in two weeks will take effect. And so it is that a person who once receives the poison is forever enslaved. Ribiera kidnaps Paula Canalejas, daughter of a Brazilian cabinet minister who, on becoming a victim, has killed himself, preferring death to "murder madness." Bell rescues Paula, and they flee from Ribiera in a plane. They find The Master's hidden jungle stronghold, and Bell destroys it with a bomb attack from the air. As he is getting away his motor quits. Paula jumps for her life, and shortly afterwards Bell follows, drifting straight down towards his enemies below. CHAPTER XI Bell was falling head-first when the 'chute opened, and the jerk was terrific, the more so as he had counted not the customary ten, but fifteen before pulling out the ring. But very suddenly he seemed to be floating down with an amazing gentleness, with the ruddy blossom of a parachute swaying against a background of lustrous stars very far indeed over his head. Below him were masses of smoke and at least one huge dancing mass of flame, where the storage tank for airplane gas had exploded. It was unlikely in the extreme, he saw now, that anyone under that canopy of smoke could look up to see plane or parachute against the sky.