25 april

The Confraternity of the Immaculate Conception contracted Leonardo and the brothers Ambrogio and Evangelista de Predis for the altarpiece of its chapel in San Francesco Grande. There are two versions: the first, of the 1480s, is in the Louvre; the second, begun in the 1490s after a fee dispute, is…

The rebel army of Li Zicheng, a former post-station attendant, broke into Beijing on 24 April. Early the next morning the Chongzhen Emperor hanged himself on Coal Hill behind the palace, the last Ming emperor to rule from Beijing.

The highwayman Nicolas-Jacques Pelletier. Dr Joseph-Ignace Guillotin had proposed one quick method of execution for everyone, whatever their rank; the surgeon Antoine Louis designed the machine.

Written in a night by the engineer officer Rouget de Lisle at the house of the mayor of Strasbourg, as a war song for the Army of the Rhine. Volunteers from Marseille sang it marching into Paris that summer and gave it its name.

David Farragut’s fleet ran past the forts below the city in the dark on 24 April and anchored off the levee the next day. The Confederacy had lost its largest city and the mouth of the Mississippi.

Louis Leroy’s satirical review in Le Charivari, “L’Exposition des impressionnistes”, took its title from Monet’s view of Le Havre harbour, Impression, soleil levant. His imaginary visitor sneers that wallpaper in its embryonic state is more finished than that seascape. The painters adopted the…

British and French troops landed at the tip of the peninsula and Australians and New Zealanders a little up the coast at what became Anzac Cove. A lieutenant-colonel named Mustafa Kemal held the heights above them. 25 April is Anzac Day in Australia and New Zealand.

British, French, Australian and New Zealand troops landed at Cape Helles and Anzac Cove. A lieutenant colonel named Mustafa Kemal threw his regiment into the heights above Anzac and held them.

Three papers in one issue: Watson and Crick’s model (pp. 737–738), then the King’s evidence from Wilkins, Stokes and Wilson and from Franklin and Gosling, with Photo 51. Watson and Crick thanked the King’s group for “a knowledge of the general nature of the unpublished experimental results”;…

As the test programme required, the emergency core cooling system was disconnected at 14:00. Then the Kyiv grid controller asked the plant to keep supplying power through the afternoon peak, and the reactor sat at half power for nine hours, its emergency cooling still switched off.

Released by the grid at 23:10, the operators brought the power down again. At midnight the shifts changed, and the test passed to men who had not prepared for it.

Aleksandr Akimov led the shift in the Unit 4 control room; Leonid Toptunov, 25, sat at the reactor controls. Anatoly Dyatlov, the deputy chief engineer, directed the test.

While control passed between regulating systems the power fell to about 30 megawatts, and the core began to fill with xenon, which soaks up neutrons. To climb back the operators pulled out rod after rod; by 01:03 they held it at 200 megawatts, far below the 700 to 1,000 the test programme set.…

Major Leonid Telyatnikov, who commanded the plant's fire station, was off duty at his dacha; called at about 01:32, he came in to lead the fight on the roofs. He survived the radiation sickness that followed, and died of cancer in 2004.

Unit 4 was to be shut down for maintenance, and on the way down the staff would test whether the turbine, coasting to a stop, could power the cooling pumps for the minute or so the diesel generators needed to take over. Earlier attempts had failed. What was planned as a day-shift job ended up on…

At 01:23:04 the steam to turbine 8 was shut off and the test began. As the turbine slowed, so did the pumps it fed; the water in the core warmed and boiled, and in an RBMK more steam means more power: the reactor's positive void coefficient.

The senior reactor control engineer, Toptunov, pressed the emergency shutdown button; INSAG-7 could not establish why. The rods moved in slowly, and their graphite tips first pushed water out of the bottom of the core, so the shutdown briefly added power to a reactor already running away.

For almost three days nothing was said in public. Pripyat went about a warm Saturday, with weddings and football, while the plant burned three kilometres away.

The wrecked core stayed hot and kept releasing for ten days. UNSCEAR puts the release at about 1,760 petabecquerels of iodine-131 and 85 of caesium-137, carried north-west over Belarus and Scandinavia and then across Europe; it fell away sharply around 6 May.

Alarms for a runaway power rise sounded at 01:23:43, and by 01:23:47 the recorders showed the cooling circuit failing. Most witnesses heard two explosions; they threw the reactor's 1,000-tonne upper shield aside and scattered graphite and fuel across the site. The reactor engineer's log reads…

The operator of the main circulation pumps was in the pump hall when it collapsed. His body was never recovered; he lies under the ruins of Unit 4.

Firefighters from the plant and from Pripyat fought more than thirty fires on the roofs of the turbine hall and the reactor building, among lumps of graphite they had no way to recognise. By about 05:00 every fire but the one inside the reactor was out.

Lieutenant Volodymyr Pravik's watch from the plant's own fire station was first on the scene, followed by Lieutenant Viktor Kibenok's crew from Pripyat. Both lieutenants were 23, and both died in Moscow two weeks later.

Believing the reactor intact, as Dyatlov and the plant's managers reported to Moscow, Akimov and Toptunov spent the early morning opening valves by hand to feed it water. The water had nowhere to go; both men received fatal doses.

A day after launch on STS-31, Steven Hawley lifted the bus-sized telescope out of Discovery’s bay with the robot arm, some 600 kilometres up, the highest orbit a shuttle had yet flown. Weeks later its main mirror turned out to be ground to the wrong shape.

At $44 billion, $54.20 a share. He tried to back out that summer, and was sued to go through with it.