Obituary: Sir James Lighthill

SIR JAMES Lighthill was a good neighbour and friend, as well as a brilliant scientific colleague, write Professor Gustav Born and Professor P. D. Richardson. May we add to your excellent obituary (by Professor D. G. Crighton and Tam Dalyell, 22 July) by recounting the sad coincidence whereby, only a few days before he died, theoretical work done by Sir James in bio- fluiddynamics, a science he pioneered, was related by one of us to experimental work done by the other about 10 years ago?

When William Harvey discovered the circulation of the blood in 1628 the only blood vessels known were the arteries which take the blood away from the heart and the veins which bring it back: connections between arteries and veins required by Harvey's postulated circulation were unknown. These connections, the capillary vessels, were only discovered in 1661 by Malpighi with the aid of the microscope, because they are exceedingly small.

Ever since then there has been the question as to how the blood manages to flow through vessels which are narrower than the diameter of the red blood cells. When being squeezed through a capillary the red cell becomes reversibly deformed but the vessel is not distended. Lighthill calculated that this is so because the lateral pressure required to deform a red cell is at least 100 times smaller than the pressure needed to distend the capillary.

This leaves the question as to the mechanism that permits the moving blood cells to slide past the static capillary walls. The exceedingly close apposition between them implies, as with tight-fitting engine pistons, the need for lubrication. Lighthill showed that resistance to movement of the red cells is very great when their speed is slow in the capillaries, where the lubricant layer of the blood plasma is very thin indeed. So might there be something else to help maintain such a lubricant plasma layer? The experiments we referred to provided evidence that the lateral force calculated by Lighthill is critically augmented by electrostatic repulsion between dense negative charges on both red cells and vessel walls.

Lighthill had an amazing range: his contributions were crucial to topics as far apart as reducing jet engine noise and the circulation of the blood.

Sir James Lighthill was an inspirational teacher, writes C. A. G. Webster. I was in his class as a final year undergraduate at Manchester during his last year at the university.

Often he would arrive in a red Heinkel bubble car so packed around with children that he had to gesticulate for someone to open the door for him from the outside in order to get out. I still hear him saying, "I can't teach thermodynamics without coloured chalk", and storming out of the lecture theatre in search of some in order to tell us about "Leoville's spiffing equation". He was a great party man and I continue to use his theorem - "A party is no good if you can move about".