In earlier life he had done good service in Ceylon, had been in the Crimea during the Russian war, and had superintended the construction of the first Turkish railway.

Then, at the age of forty, he turned his attention to African travel.  Accompanied by his wife, he left Cairo in 1861; and, after exploring the Blue Nile, arrived in 1862 at Khartoum, situated at the junction of the White and Blue Nile.  Later on he turned southward.  In spite of the opposition of slave owners, and without guide or interpreter, he reached the Albert Nyanza; and when, after many perils, he got safely back to Northern Egypt, his fame as an explorer was fully established.  His was the first expedition which had been successful in penetrating into Central Africa from the north.  On his return to England he was welcomed with enthusiasm, and received many honours.

In the year 1869, at the request of the Khedive of Egypt, Sir Samuel undertook a journey to the Soudan to put down the slave trade.

He was given supreme power for a period of four years.  In December, with a small army of about 1500 men, he left Cairo for Gondokoro, about 3000 miles up the Nile, accompanied by his wife.  It was a terrible journey.  His men fell ill, the water in the river was low in many places, and the passage blocked up.  At times he had to cut channels for his ships; the men lost heart; and, had the leader not been firm and steadfast, he would never have reached his destination.

On one occasion he found his thirty vessels stranded, the river having almost dried up.  Nothing daunted, he cut his way through a marsh, making a progress of only twelve miles in about a fortnight.  At the end of this time he found it was impossible to proceed further along that course, and had to return to the place he had left and begin again.

Still, in spite of all obstacles, he made steady progress.

At Sobat, situated on the Nile above Khartoum, he established a station, and had a watch kept on passing ships to see that no slaves were conveyed down the river.

One day a vessel came in sight, and keeping in the middle of the river would have passed by without stopping.  But Sir Samuel, having his suspicions aroused, sent to inspect it.

The captain declared stoutly he had no slaves aboard.  He stated that his cargo consisted simply of corn and ivory.  The inspector was not convinced, and determined to test the truth of this statement.  Taking a ramrod, he drove it into the corn.  This produced an answering scream from below, and a moment later a woolly head and black body were disclosed.  Further search was made, and a hundred and fifty slaves were discovered packed as close as herrings in a barrel.  Some were in irons, one was sewn up in a sail cloth, and all had been cruelly treated.

Soon the irons were knocked off and the poor slaves set free, to their great wonder and delight.

Sir Samuel arrived at Gondokoro on the 15th of April, 1871.  Already two years of his time had expired.  In addition to checking the slave trade, he had been commissioned to introduce a system of regular commerce.  He set to work at once to show the people the benefits of agricultural pursuits.  He got his followers to plant seeds, and soon they were happy enough watching for the green shoots to appear.