| Hi All, I have managed to get together some details regarding the body parts of Elizabeth Jackson found floating in the Thames. It is all based upon the best information I can find and I apologise if it is a littlelong winded. I should point out that I have no practical knowledge of sailing on the upper Thames, the farthest I ever got was from seawards to Deptford. Any boatman or yachtsman with experience of the upper Thames may be able to add further information and should such a person chance toread this post, I would welcome their comments. Anyway, here goes.... ELIZABETH JACKSON Any attempt to track the movement of body parts immersed in a tidal river will need to consider the different forces that may cause or impede movement, so first let us consider the forces involved. BOUYANCY A complete human body would first of all sink to the river bed and as decomposition takes place gases would build up inside the body until it eventually rises to the surface; this takes between two and four weeks. In this case the body was cut into several parts and due to the fact that medical reports suggest that the first body parts recovered had been in the water for about 24 hours buoyancy can be assumed. There are three states of buoyancy; positive buoyancy were the object floats on the surface, neutral buoyancy were the object floats below the surface and negative buoyancy were the object sinks to the bottom. The recovered body parts would have been of positive or neutral buoyancy, although the head – which was not recovered – would I think have been negative buoyancy. I have little medical or anatomical knowledge but a human head is said to weigh about 10-12lbs. and is composed of a lot of bone, therefore I think that the density would have been greater than the other body parts thus causing it to sink. WIND Any object floating on the surface may have its direction influenced by the strength and direction of the wind, a wind from the east would cause the object to move in a westerly direction whilst a wind from the north would cause movement to the south. Weather reports published in the Times for the dates in question suggest very light winds from a generally northerly direction; therefore I believe that these would have little effect on the speed and direction of travel. TIDES The river Thames has two tides a day, that is to say that the cycle of low water to high water and back to low water, happens twice in approximately 24 hours. Each high or low tide occurs progressively later than the last by about 30 minutes, for instance on 9th June 1889 high tide occurs at 09.58 and 22.28, and on 10th June 1889 high tide occurs at 11.03 and 23.32. At high or low water there is a short interval, usually about 30 minutes, when the tide does not travel in either direction, this is known as “slack water”. There are two types of tide which alternate roughly weekly and are known as “spring tides” and “neap tides”, at spring tides the tide rises higher and settles lower than at neaps and this also causes the rate of flow, or current, to be greater on springs than on neaps. The tidal heights predicted for 4th June 1889 are 5.5 meters falling to 5.0 meters on 7th – 8th June, on 9th June they increase to 5.3 meters rising to a maximum of 6.5 meters on 15th June. We can therefore say that the period 4th -10th June was a period of neap tides. Incoming tides which in this case travel from east to west are known as “flood” tides, whilst outgoing tides known as “ebb” tides travel in the opposite direction. Tidal predictions are based on phases of the moon and are generally accurate, however certain weather conditions can cause a variation of the time and height of a tide; strong northerly or north easterly winds and low barometric pressure in the North Sea between Scotland and Norway can cause higher tides and a stronger current on the flood. Recent heavy rainfall can cause storm water to drain through the river giving higher tides and stronger ebb tides. Equinoctial tides will also give higher and stronger flood tides. However there is no evidence to suggest that any of these factors came into play during the period we are concerned with. The current of any tide is not constant, it rises gradually from zero to its maximum at half flood or ebb, and then reduces gradually to zero as high or low water is achieved. I have checked all available resources for further information on tidal streams between London Bridge and Teddington but have found no useful information given beyond a point between Southend and Sheerness, we shall have to rely on the following information from Reed’s Nautical Almanac: Tidal Stream Rate [maximum]. London Bridge: Flood – 2.5knots Ebb – 3.5knots. Tidal Ebb and Flood [average] London Bridge Ebb- 6hrs. 32 mins. Flood – 5h.55min OBSTRUCTIONS There are several possible obstructions that could delay movement of a floating object, these include jetties, wharves, bridge piers and vessels anchored in the river; the suction or wash from a passing steamboat may also have an effect. Bends in the river although not an obstruction will cause the tide to set to the outside of the bend. THE FIND AT HORSLEYDOWN We do not have an exact time that the body parts were found at George’s Stairs but from the information we have it would seem likely that it was sometime about midmorning. The distance from Albert Bridge to George’s stairs would be approximately 4.7 nautical miles and the body would have to travel on an ebb tide. To decide the speed that the body part would travel at, consider that maximum speed of 3.5 knots would be at spring tides, but on the date in question neap tides were occurring and this would give a slower maximum speed of about 2 knots. The tide does not move at this speed all the time but starts from zero at high water and increases for the next three hours or so and then starts to decrease in speed until low water is reached. Therefore let us assume an average speed of 1 knot. High water at Albert Bridge on 4th. June 1889 occurred at 05.16hrs., taking the assumed average speed it would need 4 hrs. 45mins. to travel the 4.7 miles from Albert Bridge to George’s Stairs, this gives an arrival time of 10.01hrs. George’s stairs were on the south side of the river opposite St. Katherine’s Dock and this would be in keeping with the northerly breeze mentioned earlier. This model suggest that the body parts were placed in the water around 4-5am, a time when the area may have been at it’s most quiet. As soon as time permits I intend to attempt to plot the course of the other remains if anyone wishes me to do so. Rgds John |
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