Poynting and Birmingham
During a recent visit to Birmingham University, I spotted a blue plaque commemorating physicist John Henry Poynting.
Zooming in on the blue plaque, we see that Dr Poynting is celebrated on this building for having measured the mass of the earth.
You can’t put the earth on a set of scales, but you can use precision balances to measure the gravitational effect of objects on each other, and use that to calculate the mean density of the earth. From that, you can calculate the mass. Poynting spent 12 years at Cambridge and then at Birmingham carrying out these experiments. Although that is what the blue plaque records, it is some of his other work which resulted in his name being being well known to physicists.
Dr Poynting was the first Professor of Physics at Birmingam University, when it was formed under that name in 1900. He had been heavily involved with the university’s formation, having been a professor at the Mason Science College, effectively a predecessor organisation before Queen Victoria issued the Royal Charter to Birmingham University in March 1900.
Poynting had worked at the Cavendish Laboratory, Cambridge under James Clerk Maxwell, one of my scientific heroes. After Maxwell died, Poynting was one of a group of physicists who collaborated to rework Maxwell’s equations of electromagnetism into their familiar form.
Professor Poynting developed an expression for an entity familar to all physicists which is known as the Poynting Vector. This, as its name suggests, is mathematically a vector (i.e. it has a direction as well as a size). It is the magnitude and direction of the energy flow in an electromagnetic field or electromagnetic wave. Electromagnetic waves include light of all colours and wavelengths, radio waves, infra-red light, ultra-violet light, X-rays, and some forms of radioactivity.
S = E x H
Poynting Vector S in terms of electric field E and magnetic field strength H. “x” denotes the vector “cross” product
In an EM wave, the electric field and magnetic field are at right angles to each other and the energy flow (the Poynting Vector) is at right angles to both of these. Poynting established also that electromagnetic waves, including light, exert a pressure on a surface they hit, and the greatest pressure is to be found in the direction of the Poynting Vector.
Poynting’s life and work brought him into contact with many of the other most famous physicists of his time. I have mentioned Maxwell above. After leaving Cambridge, Poynting spent some time teaching at what would become Manchester University. One of his students was JJ Thomson, later famous for discovering the electron. One of my own most inspirational teachers encouraged his classes to refer to Thomson as JJT as if we all knew him personally!
Dr Poynting and JJT collaborated on a physics text book which was still in print half a century later. This book was rather modestly entitled “A Text Book of Physics”, but was in very widespread use in Physics teaching.
Although non-Physicists may not have heard of Professor Poynting, his work on electromagnetism and EM waves amongst other subjects was a hugely important contribution to knowledge in the latter part of the 19th Century and the early part of the 20th.
Mind the Gas
Fumigation of ships and cargoes has for many years been a source of problems to ship and cargo owners. Recently the UK MAIB issued a preliminary report into a serious incident on the vessel THORCO ANGELA, which happened in Liverpool in October 2021.
Insects are a fact of life. The Royal Entomological Society estimates that there are around 1.4 billion insects per each human alive on earth. The total mass of insects on earth is, they estimate, around 70 times the mass of all of the humans.
Hardly surprising then that agricultural cargoes (grains, oilseeds, animal feeds, etc) are at risk of becoming infested. Nobody wants that, and to avoid infestation cargoes must be treated every few months.
Insecticides can be sprayed onto a surface or cargo (“contact insecticides”) or can be applied as a gas (fumigants). Treating a large bulk with contact insecticide would require it to be sprayed (for instance) onto cargo on a conveyor. Using a fumigant is often more convenient as the gas can penetrate a large bulk.
The disadvantage is that it takes time for fumigant gas to diffuse throughout a large bulk. If in that time the gas starts to leak out, that’s bad for two reasons. Firstly, the fumigation may not be sufficiently effective (because the gas wasn’t present throughout the stow for long enough). Secondly, and much more important for safety reasons, if the gas isn’t staying the holds, it is going somewhere else. Fumigants are used because they kill insects. They can also kill humans or at the very least make them very ill indeed.
Most fumigation on ships these days uses a fumigant gas known as phosphine, chemically PH3. With very few exceptions this is deployed on ships by introducing solid preparations (tablets or pellets etc) into the hold. These solid materials contain aluminium or magnesium phosphide. These chemicals slowly react with atmospheric moisture in the hold and release the phosphine gas itself.
Phosphine is very dangerous. The recommended limit for spaces occupied by humans (NIOSH time weighted average) is 0.3ppm. But it isn’t just the toxicity. Phosphine is highly flammable in air, and in the real world, impurities commonly found in it can make it spontaneously explosive. Hatch covers can and have been blown into the air by phosphine explosions. The solid materials themselves can cause fires if they become wetted.
Fumigation on ships is, for these reasons, subject to IMO rules, recommendations and regulations. The IMO publication “Recommendations on the Safe Use of Pesticides on Ships Applicable to the Fumigation of Cargo Holds” has quite an unwieldy title, but contains guidance which should always be followed to ensure safety of life and vessel. This publication can be found as IMO Circular 1264, but it is also bundled as part of the IMSBC Code.
One part of the safety requirements is appropriate signage to indicate when fumigants are in use.
Standard shipboard gas meters are not designed to detect phosphine gas (although they have a sensor which may be referred to as a “toxic gas” sensor, they won’t help in keeping personnel safe). Specialist electronic meters exist, but they are quite expensive and no use for other tasks. Inexpensive glass detector tubes (made by Draeger or Gastec or similar) can be used but each tube can only be used once so you would get through a lot of such tubes in any particular practical deployment.
Lots of articles have set out the provisions to be found in IMO Circular 1264. I’m not going to do that here but I am going to discuss a point which came to the fore during the lockdowns applied as part of the worldwide response to the Coronavirus pandemic.
In the Circular, the following paragraph can be found.
Since fumigant gases are poisonous to humans and require special equipment and skills in application, they should be used by specialists and not by the ship’s crew.
IMO Circ. 1264. Para 3.1.2.2
Recommendations on the Safe Use of Pesticides on Ships Applicable to the Fumigation of Cargo Holds.
This provision is very clearly worded. The pandemic however caused all sorts of problems with many aspects of world trade. One particular trade customarily posted a trained fumigation operative to sail with a vessel as a supercargo. One of his duties was to monitor gas levels in the holds and add more solid phosphide preparation into the holds to “top up” the gas levels. I presume (or hope!) he would also carry out checks to establish where the gas was going, and to ensure that wasn’t going to cause problems.
With the Covid pandemic, this was no longer allowed. Getting personnel on and off ships became virtually impossible in many instances, and so a supercargo riding with the vessel was no longer viable.
The shipping world is full of “make do and adapt” attitudes – admirably so in many instances, but not here in my opinion. Initially, crews were supplied with the solid materials and asked to top up when required. No doubt this was done without incident on a number of occasions but it does violate the IMO Recommendations. As consultants we did not recommend carrying this out.
A second level of “work-around” was developed in which fumigation companies provided specific training to a designated crew member who thus became a “specialist”.
The organisations which were involved in this trade were relatively sophisticated and no doubt took this training seriously. However, once a precedent is created in which crew members are handling fumigants and fumigation materials, there becomes a possiblity that problems may arise if untrained crew members become involved.
Turning to the THORCO ANGELA incident (note, Sheard Scientific were not involved in investigating this), the MAIB report indicates that she loaded sweet potato in Rizhao, China. MAIB concluded that trained fumigators had not been allowed on the vessel and nor were any crew members supplied with sufficient training or equipment.
MAIB also conclude that the deployment of the solid phosphide material was done in such a way that the fumigant phosphine did not adequately “volatilise and disperse”. If the solid phosphide materials still contain substantial unreacted phosphide at the end of a voyage, they will still have the propensity to give off fresh phosphine gas.
One of the stevedores involved in discharging the cargo from THORCO ANGELA became unwell and was taken to hospital suffering with nausea, loss of balance, and nerve damage to his hand. MAIB note that Liverpool port had not been informed that the cargo was under fumigation. Thus the stevedores had no advance warning that there might be a problem.
This was undoubtedly a very serious incident, and it could easily have been very much worse. The takeaway lesson for those involved in carriage of cargo under fumigation should be to ensure that where alternative procedures are introduced (perhaps because there was no alternative), all effort should be made by all parties to make those alternative procedures as safe as the original ones. If ship’s crew are going to carry out the tasks which should be carried out by specially trained personnel, that can only take place if the crew members in question genuinely have received sufficient training.
A trip to Whitby – Dracula, Captain Cook and the Scoresbys
A younger member of the Sheard household is studying literature (and fancies herself a bit of a Goth), so we had a trip to Whitby in North Yorkshire to see what we could discover about Bram Stoker’s inspiration for Dracula.
Vampires aside, Whitby of course has a proud maritime history. Captain James Cook was born and lived nearby and explored huge previously uncharted parts of the world.
The focus of our trip however was Dracula, written by Bram Stoker, a frequent visitor to Whitby.
In the story, Dracula arrived at Whitby by sea and some of the novel is set in the graveyard of St Mary’s Church, near the Abbey.
Wandering around the churchyard, we didn’t find any vampires but we did find numerous Master Mariners. Many of the graves are actually memorial stones to those lost at sea.
Nearby in the churchyard, however, we located something of significant interest historically and scientifically – the grave of William Scoresby.
William Scoresby made his fortune in Arctic whaling. He is often credited as the inventor of the ship’s crows nest. Elevated lookouts on ships may have existed prior to Mr Scoresby, but he apparently did originate the barrel crows nest.
In the church itself is a chair known as the Scoresby Chair, which was carved from the remains of the vessel ROYAL CHARTER, on which William’s son, Rev William Scoresby carried out scientific experiments.
Rev William Scoresby spent many years working on the problem of compass deviation on ships incorporating iron as part of their structure. His views brought him into conflict with the Astronomer Royal, Sir George Biddell Airy with such vehemence that the issue became known as the Airy-Scoresby Controversy.
The problem is that iron in a ship’s structure can become magnetised and interfere with the operation of a navigation compass. Numerous ships were lost as a consequence.
Airy proposed a solution in which the ship would be “swung” through the points of the compass and the behaviour of the navigation compass checked at each orientation. Iron masses were then added in the vicinity of the compass to neutralise empirically the effect of the iron ship structure on the compass readings.
Scoresby believed this approach was so wrong as to be dangerous, and said so during a speech he gave to the British Association for the Advancement of Science in Liverpool. He believed the magnetic effect of the iron in a ship’s structure could suddenly and unpredictably change as a consequence of the vibrations set up by her motion in a seaway.
To investigate this, Rev Scoresby sailed around the world via Australia on ROYAL CHARTER in 1856 and took a large number of compass readings during the voyage. He aimed to demonstrate his theory of shifting magnetic influence by means of these observations.
Rev Scoresby died in 1857, and ROYAL CHARTER sank in 1859. The outcome of the controversy was that Airy’s system of compensating massess was retained, but one of Scoresby’s innovations, locating a “pole compass” on a mast and away from the ship’s iron structure, was incorporated to improve maritime safety.
A small part of ROYAL CHARTER lives on in the Scoresby chair and if you visit Whitby, I suggest you take a look.
