Yesterday’s papers reported on a letter to Nature showing a negative correlation between global temperatures and the Sun’s emission in certain wavelength bands. This is of obvious importance since it appears to cut the ground from under the feet of those who blame global warming on changes in the Sun. So I turned eagerly to Nature to see the original.

I went first to the report in their “News & Views” section, and found this:

The SIM observations show very large increases in irradiance for the years 2004 minus 2007 at ultraviolet (UV) wavelengths, together with sizeable decreases at wavelengths longer than 400 nanometres, in the visible range.

To prove that it was not an accident, they repeat the mistake twice more in the article.

Don’t they care?, I thought.

Actually I do something similar (but maybe less bad) quite frequently.

TeX, which is more than thirty years old, has simple commands for a hyphen, an en-dash, an em-dash, and a minus sign. (The en-dash and em-dash have lengths an en and an em respectively, measures in typesetting based on the width of the capital letters N and M.) Beginning students sometimes don’t know which to use, but anyone who writes about the Engeler–Ryll-Nardzewski–Svenonius theorem has to know the difference between a hyphen (separating parts of a word or name) and an en-dash (separating distinct words or names). Em-dashes separate parts of a sentence — rather like a pair of brackets — though I am not quite sure whether there should be space around them or not.

After all this time, computers are still much more restrictive than traditional typography. We can produce professionally typeset PDF files using pdfLaTeX, but HTML still lacks both the symbols and the fine spacing commands that are vital for mathematics. WordPress allows us to include compiled LaTeX formulae in text, but for me the badness of mixing entirely incompatible typestyles in a sentence outweighs the advantage of being able to typeset the formulae accurately. So I write all the mathematics on this blog in HTML.

Problem is, there is no minus sign in HTML, so I have to use an en-dash for the purpose. There is also no way I know to implement the rule used in TeX that there should be a bit more space round a relation sign like = than around an operation sign like +. It is all or nothing, an entire non-breaking space, or no space at all. So a typical formula looks like a+b = c. Equivalently a = cb, where I have used an en-dash in place of a minus sign. In an exponent, I can then use a hyphen for a smaller minus sign: 2a = 2cb.

In extremis I would write out the name of the TeX command for a particular effect, as in {n choose k}, and hope that it was comprehensible.

But I hope I will never be driven to writing out “minus” for an en-dash…


About Peter Cameron

I count all the things that need to be counted.
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4 Responses to Oops

  1. D. Eppstein says:

    There is too a minus sign in html. It’s −.

    • Thanks, I stand corrected. Actually you can do any Unicode character in HTML, but WordPress doesn’t recognise most of them (as I discovered in an earlier post when I had to mention Gothic characters). I was too lazy to try the minus sign, but let’s do it now. It is character 2212 (hex): so ab = c.

      It works.

  2. Matt Fayers says:

    In response to your “I am not quite sure” about the em dash: my understanding is that for a dash used as punctuation in this way, one should use either an em-dash with no surrounding spaces, or an en-dash with surrounding spaces. However, the former option seems to be going out of fashion these days, so perhaps the em-dash is on its way to obsolescence (just as the hyphen is in America).

  3. Jair says:

    I prefer to imagine that em-dashes are named after Emily Dickinson, who put them to such good use.

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