A quick quiz for those intimidated by Mathematics. What is the ratio of the circumference of a circle to its diameter? Pi, you may say. Numerically, it is 22/7, most may agree. But, it is an irrational number, math whiz kids will protest. For those decimally oriented, the value of Pi translates into 3.14. But that too is an approximation, the sticklers will object. It is a non-recurring decimal. The value of Pi correct to 10 decimal places is 3.1415926536.
Ten-year old Aditya can remember the value of Pi correct to 20 decimal places. Not a great feat, incidentally, considering that the value has been calculated correct to several thousand decimal places. But how does Aditya do this? He just remembers the doggerel:
Sir, I know a rhyme excelling
In sacred truth and rigid spelling
Numerical sprites elucidate
For me the accurate-most amount.
That is an example of a mnemonic: a device, such as a formula or rhyme, used as an aid to remember facts. The classic mnemonic, of course, is the one that goes "30 days hath September, April, June, and November."
Trigonometry is a bugbear for beginners. We all know that Sine, Cosine and Tangent are ratios of two sides of a right-angled triangle, but which is which? Help is at hand: just remember: "The Old Arab Carried A Heavy Sack Of Hay." The initial letters in groups of three represent "Tangent = Opposite / Adjacent; Cosine = Adjacent / Hypotenuse; and Sine = Opposite / Hypotenuse." Can anyone make it simpler than that?
The greatest use of a mnemonic is for remembering the order of things like the planets and the twelve disciples of Jesus Christ. For those who find it hard to remember the BODMAS rule, it is easy if you memorise "Buzz Off, Daisy, Mary And Sarah" and you have "Brackets, Of, Division, Multiplication, Addition, Subtraction" in the right order!
It is not as if mnemonics are used only in mathematics. The initial letters of the sentence "My Very Educated Mother Just Showed Us Nine Planets" helps you recall the names of the nine planets in the increasing order of their distance from the Sun — Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.*
In Biology, the animal kingdom (and the plant kingdom) is divided and subdivided. The hierarchy is not easy to remember, but the sentence "Kids Prefer Cheese Over Fried Green Spinach" comes to our rescue. The initial letters represent the classification: Kingdom, Phylum, Class, Order, Family, Genus, Species. A variation is "King Philip Came Over For Good Sleep." Talking of royalty, `King Henry Died Gently Drinking Chocolate Milk' signifies Kilo, Hecta, Deca, Grams (or meters, litres, hertz, watts, bytes or whatever) Deci, Centi and Milli.
The six wives of Henry VIII were Catherine of Aragon, Anne Boleyn, Jane Seymour, Anne of Cleves, Katherine Howard and Kathryn Parr and they all met with different ends. History does not record if he faced any difficulty remembering their names but we have a rhyme to remember their end: 'Divorced, Beheaded, Died, Divorced, Beheaded, Survived'!
This rhyme is to remember the names of the twelve disciples of Jesus: "This is the way the disciples run:
Peter, Andrew, James and John,
Phillip and Bartholomew,
Thomas next and Matthew, too.
James the less and Judas the greater;
Simon the zealot and Judas the traitor."
Some mnemonics are quite interesting. The credit-card sized slot found mostly on portable computers for cards such as modems and network interface devices had an incredibly long acronym PCMCIA, which stands for Personal Computer Memory Card International Association. A mouthful, isn't it?
Most of us cannot memorise the acronym, leave alone its expanded version. "People Can't Memorise Computer Industry Acronyms" is as good as mnemonics can get!
Orthopaedic doctors might find it useful to remember "Some Lunatics Try Professions That They Can't Handle" for the order of the bones in the wrist: Scaphoid, Lunate, Triquetral, Pisciform, Trapezium, Trapezoid, Capitate, Hamate. Whew! One needs to take a big breath to say all that!
Some people scoff at the attempt people make to remember some `inane-sounding sentence' just to remember something else you already know; but then do they realise the fun they are missing out on?
*Obviously, this was well before August 2006 when Pluto was demoted.