He kept a Medical Journal from 21st May 1832 while the vessel is still at Deptford being fitted out.
They were fortunate in totally escaping from the prevailing cholera, although the Surgeon was puzzled as to why this should be. The Guard embarked under unfavourable conditions and were drenched. The weather continued so damp that they could not be kept dry and some became ill........ We were unfortunate in embarking one case of phthisis who did not raise suspicion; these men are so anxious to get away from the rigid discipline of the Hulks that they endeavour to conceal their complaints. He was however, soon obliged to apply to the Hospital but the progress of the disease was rapid and fatal.
Henry Tanner 1834
Medical Journal from 4th June to 14 November 1834.
During the voyage, two deaths occurred, the first a case of mania occurred off the Cape of Good Hope after only a fortnight's illness. John Edwards was unable to perform a post mortem because of bad weather. The other death, that of Edmond Smith was caused by phthisis. Smith was ill before he embarked and John Edwards noted that at the time of inspection at Woolwich, he appeared debilitated and wan but as both Smith and the Woolwich surgeon said there was no illness he could not be rejected.
After sailing, the surgeon discovered that Smith had a troublesome cough and had been ill for some time, but concealed his illness as he wished to be taken on the Henry Tanner as his brother was also on the same vessel. The Surgeon cared for Edmond Smith until Smith finally passed away on 29th August.
Roslin Castle 1836
Medical Journal from 15 September 1835 to 14 March 1836.
This was his third voyage as Surgeon Superintendent and only one bringing female convicts. He considered the women who embarked on the Roslin Castle to be of the worst description he had seen, both morally and physically......
A more filthy, indolent and reprobate set of women were never expatriated. Most had been in prison more than a year and many were sent from the hospital as incurable.
There were a total of 182 women and 49 children on the voyage, 17 of them were free women and 23 of their children. Adverse weather increased the sea sickness at the start of the voyage and many of the women suffered the consequences even after the bad weather ceased.
There were many long-lasting cases of gastric irritability and some of the old women were nursed all through the voyage. Obstinate obstruction of the bowels was also a general consequence, made worse by the women not reporting it for 10 or 15 days. The bowel conditions were made worse by the change in diet from the low hospital diet to the ship's dry provisions and by existing diseases from leading dissipated lives.
'A week after leaving harbour one of the women died of fever which caused a great alarm among the women. This at least did have the effect of encouraging the prisoners to keep themselves and the prison clean, 'although even after this, from time to time, the filthy habits of some among them in the night about the water closets was a source of great annoyance to the people in the contiguous berths and of anxiety and vexation to myself'.
Three women in total died as well as four infants. Few of the women became reconciled to their new diet, they especially objected to cocoa and after a few days it was thrown away and tea substituted; even this did not suit some who had never had tea before. They had an incessant, almost morbid, longing for potatoes, for which they would have sacrificed everything else.
Charles Kerr 1837
John Edwards' medical journal is interesting in that it reveals some of the convicts' thoughts and fears - Richard Edwards who was weighed down with guilt and James Dent who died on the 18th August. The indents don't reveal whether James Dent could read or write, many on the ship could not, but when he became delusional with fever, he revealed to the surgeon his greatest fears.....he dreamed he had been removed from the ship by magic and taken by the bushrangers of New South Wales where he witnessed horrific transactions. The surgeon could do little to convince him otherwise. James Dent died at the most unfavourable portion of the passage when a succession of heavy gales hit the ship.
The storms lasted for 12 days and there was almost constant rain and the frequent shipment of heavy seas kept the vessel above and below continuously under water preventing anything approaching dryness or ventilation in the prison and hospital. Besides this the upper seams near the side let in the water so abundantly that at one time there was not a dry bed in the hospital - many of the berths in prison equally sharing in the discomfort. After this the weather improved and they completed the remainder of the voyage without any more serous sickness.
Later Naval Service
John Edwards was appointed Surgeon to H.M.S. Excellent on 6 February 1840. H.M.S. Excellent, Captain Sir Thomas Hastings, was built at Portsmouth in 1810 and was 2155 tons. 
He was appointed to the William and Mary yacht in September 1843