The occasion was the setting of the foundation stone for the new town hall.
When Portsmouth was raised to the status of a city in 1926, it became the Guildhall.
The new town hall, built at a cost of £137,098, was opened by the Prince of Wales on August 9, 1890.
The foundation stone had been laid four years earlier by the mayor, Councillor Alfred Blake, on Thursday, October 14 1886.
Cut from Withed Quarry, Portland, it weighed two-and-a-half tons. Beneath the stone was buried a scroll signed by all the council. The white building seen to the rear/right of the photograph is the premises of a Shepherd & Son, railway carriers.
This building would be roughly where the Central Library is today.