Recent & not so recent
additions & corrections


2018-07-11.  More has been added to the article on Converting an existing bike to an e-bike . The article first appeared on 2018-05-06.

 2018-03-17.  The camerasunderwater info collection has now been transferred to this website. See the Photography and Optics section.

 2018-02-08.  For those who notice such things, it will be apparent that I have decided at last to bring my HTML writing methods into the 17th Century.  I started writing this website in around 2000, using a piece of software called 'Adobe Pagemill.'  Pagemill produced terrible HTML (what the hell is a 'naturalsizeflag' ?), but it had some very clever features that were not replicated by later programs. Particularly, it had a link checker and manager that allowed files to be relocated; i.e., a file could be moved to a new folder and all the pages linking to it would be updated accordingly.  That allowed the maintenance of a logical data hierarchy, which is a serious bonus in a site with as many files as this one.
     Pagemill was never updated to keep abreast of new HTML standards because Adobe first replaced it with a horror called 'GoLive', which wanted to kidnap the victim's website and imprison it in a databse, and then acquired a piece of software called 'Dreamweaver'.  Giving GoLive a miss for obvious reasons; I tried editing my website using Dreamweaver, but quickly discovered that the dream was a nightmare.  I had produced many of my page layouts by using tables.  Dreamweaver however insisted that all data in every table cell needed to be contained within a paragraph, so would insert <p> at the beginning of each entry and </p> at the end.  This was not required by the 4.01 rules, but any attempt to delete these spurious tags would result in them being reinserted when the file was saved.  So, opening a file in Dreamweaver and then saving it had the effect of utterly destroying the layout.
     At the time of meines kampfes mit Dreamweaver, there was talk of new browsers that were not going to support old HTML standards.  The idea, in the minds of the individuals promoting this approach was, presumably, that people would be able to come back from the dead to re-edit their work.  I started to panic, and tried out various other editors, but there seemed to be none capable of editing pre-existing pages without wrecking them.  All insisted that the user had to do it their way, and the orthodoxy seemed to be that no web page actually needed to have any significant content; so it was obviously necessary to force vast amounts of blank space.
     So eventually, I gave up and carried on using Pagemill, while slowly converting pages into pdfs and dreading the point at which browsers would cease to parse my HTML.  That problem, of course, never happened; firstly because all of the people who had died since the beginning of the Internet proved to be disinclined to update their markup, but mainly because the idea of excluding legacy code is idiotic.  To do such a thing would be software project suicide, because it results in a browser that can't browse.  Deprecated coding methods are not secret, and so it's obvious that a browser just has to render what it gets.  The rather wonderful Internet Archive Wayback Machine, for example, somewhat depends on that facility.
     But there comes a point at which even I have to admit that a piece of software is too old. Indeed, Pagemill now has to be run under Wine, or in an XP Virtualbox.  So I started looking around and reading software reviews, and discovered that the horrors of the early 21st Century have mostly gone away.  Checking for broken links, for example, can be accomplished by means of an online link checking service (e.g., and, better than Pagemill, these services check both internal and external links.  Furthermore, there are now HTML editors that don't wantonly destroy pages they didn't create.  
     One such editor is Nvu, a free WYSIWYG for Windows, Mac and Linux.  It gets good reviews (with some reservations - see, eg., sitewizard), but the real $64k question that reviewers fail to address is: "What happens when you open and save a 20 year old page?"  In the case of Nvu, the software corrects any glaring errors and declares the code, somewhat optimistically, to be HTML 4.01 Transitional (i.e., in this case, very loose).  Also, having performed this automatic conversion, it does not assume that the page needs to be saved unless the user also makes a change.
     By making a minimal non-rendering change in (say) the page header, it is possible to save the file and see what the conversion has done; and the glorious and unprecedented result is that the page looks exactly the same as it did before (in Chrome and IE at least).  Now, suddenly, I find that it is possible to update old pages without re-writing them from scratch.  It's a wonder that other development teams had not thought of this.  Moreover, should you go into source mode and delete changes made by the software, they actually stay deleted (provided that the code remains internally consistent).
     So, with thanks to the Nvu team, the pages in this site can now be updated as and when they need editing; and the source will then be seen to declare (in the sense of 'Lies, Damned lies, and statements of conformity') that it is HTML 4.01.


2017-08-17. Started porting optical & photographic articles from the Cameras Underwater Info website.


2016-05-13. The English translation of Paul Drude's 1902 paper "On the construction of Tesla transformers: Period of oscillation and self-inductance of the coil." Can now be downloaded from and cited accordingly: arXiv:1605.04196 .

2016-05-09. Self-resonance and self capacitance of solenoids. v 1.00
Coils terminated by a parallel impedance behave differently from coils operated with one or both ends open circuit (vertical antennas, Tesla coils, helical resonators). The troubled history of self-resonance and self-capacitance modelling is due to the unrecognised impossibility of analysing these two very different situations using the same formulae. This article demonstrates that standard helical transmission-line theory does not apply in the uniform current case, and that it also needs considerable extension if it is to be applied properly to free coils. A new semi-empirical free-coil model is based on an Ollendorff helical transmission line terminated by its own axial field and fringe field capacitances. The author's well known 2008 update of Medhurst's formula (CL-DAE) remains valid.

2016, Mar 9th: Solenoid self-resonance measurements by Alex Pettit, KK4VB.
Added information on the use of a neon bulb array to visualise fields. Some changes to the discussion in view of work on the main self-capacitance and self-resonance article.

2016, Mar 6th: Bob Weaver has a new article on the Geometric Mean Distance method for calculating inductance, including the first ever estimation of the error inherent in using it. He also introduces the use of Monte Carlo methods as solution to the mathematical intractability of many GMD determinations.

2016, Feb 14th: I have issued a new version of Notation Symbols and Abbreviations (1.09). Despite the IOP guidelines, I have not (yet?) made the decision to put all mathematical variables in italic type, but I am in the process of eliminating any difference in meaning between plain and italic symbols. All articles with version dates after Feb. 14th 2016 will reflect this change (although few are actually affected). The main issue was that in some documents I had used an italic form to represent a quantity per unit length. I had thought of creating new symbols to get around this early bad decision, but actually it is easier and less confusing simply to put length into the equation, e.g., resistance per unit length becomes R/.

2016, Feb 4th: A new version of Solenoid Inductance Calculation is available (v 0.20). There are some minor additions and a partial re-write of the introduction. Most of the changes are to the typesetting and layout of equations. The work is still unfinished.

2016, Jan 1st: A new (still unfinished) draft of Diode detectors for RF measurement is available (v 0.09).


2015, Nov 27th: A reworking of the complementary follower detector by Patrick Turner. A full discrete component op-amp circuit with long-tailed pair for NFB gives -3 dB @ 10 MHz.

2015, Nov. 16th: Updated version of Inductor resonance experiments article.

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