Time ball at Sydney Observatory

Made by Maudslay, Sons & Field Ltd in London, England, 1858.

The time ball at the top of the tower at the front of the Observatory was the reason for the establishment of the Observatory and so is of great significance.It is still in its original condition apart from the addition of an electrical motor and some improvements made by HC Russell in the 1870s.

Before radio the only way to convey accurate time was through a visual signal. Accurate time was especially important to ships setting out on a long voyage as they needed to adjust and calibrate their ...


Object No.


Physical Description

A yellow and black time ball made of cast iron, with a cyliner, piston, rack and pinion lifting mechanism, safety lock, electric motor and ball.

Observatory stock numbers 9 and 10.



15.6 m



The Time Ball consists of a cast iron cylinder, piston, rack and pinion lifting mechanism, safety lock, electric motor and ball. The cylinder is 30cm diameter and 3 m long. Approximately 7 liters of soapy water fills the bottom of the cylinder to act as a buffer for the piston. The piston is a 10cm thick block of rubber with a bleeder valve to adjust rate of descent. The rack extends from the piston to the Time Ball and is 7.5 meters long. A pinion engages into the rack by a slide gear, which enables the electric motor to raise the rack. A large hand wheel is also attached with a pawl gear to prevent back-slipping. The Time Ball is attached to the top of the rack and is raised 2.7 metres.

At 6 minutes to 1PM the pinion is engaged into the rack and the electric motor switched on. It takes approx 2 minutes and 50 seconds to raise the ball to the top of the mast. The safety lock is then engaged and the pinion is disengaged. At precisely 1PM a signal from the atomic clock disengages the safety lock, causing the Time Ball to drop. It drops approx 2 metres immediately and the back pressure in the cylinder causes it to drop the remaining distance at a slower rate.

Carey Ward 10.3.83


Maudslay, Sons & Field Ltd 1858



The Observatory site was originally chosen because of its visibility from the harbour. The original plan was for a building to contain only the Time Ball and transit instruments, to provide a time service. The Time Ball was first dropped at mean Noon, 5th June 1858. By dec 1858 it was being dropped at 1PM as it has ever since, except Sat, Sun, and public holidays. The purpose of the Time Ball was so that ships could readjust their chronometers after spending long months at sea. At the same time the Time Ball was dropped a cannon was fired - the cannon was at Dawes Point from 1858 to 1906. It was then fired from Ft Denison, beginning on 9th Feb 1906 and was last fired on 7th Feb 1942. An electric motor was later fitted to aid in raising the ball, which was previously done by hand.

The time ball requires very little maintenace . The water is changed at 2 monthly intervals and takes 3/4-1 hr. At the same time the piston is cleaned. Lubrication of the gears is performed daily during its normal function. Powered by a 3/4 hp, 3 phase electric motor which is only on for 3 minutes daily.The job of raising the Time Ball was previously the duty of the caretaker, but since his retiremnt it is now the duty of the scientific instrument maker. The labour involved is 15 mins a day and 1hr every 2 months for maintenance. Is in generally good condition for its age

Carey Ward 10.3.83

Cite this Object


Time ball at Sydney Observatory 2018, Museum of Applied Arts & Sciences, accessed 16 October 2018, <https://ma.as/232664>


{{cite web |url=https://ma.as/232664 |title=Time ball at Sydney Observatory |author=Museum of Applied Arts & Sciences |access-date=16 October 2018 |publisher=Museum of Applied Arts & Sciences, Australia}}
This object is currently on display at the Sydney Observatory.


This object record is currently incomplete. Other information may exist in a non-digital form. The Museum continues to update and add new research to collection records.

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