A CLUE about why modern relationships are so volatile may be that women's partner preferences vary according to the time of month, in an age when commitment is no longer paramount.

That's one of the intriguing possibilities being investigated by psychologists at St Andrews University, who are mulling over responses to a Tomorrow's World survey about what sort of faces turn us on.

The survey suggests that women may be influenced by different physical and personality characteristics in partners at varying times of their menstrual cycle.

A Despairing note is struck by Jack, a Samaritan from Perth who wrote to Which? magazine following a survey that valued charities in financial terms.

Says Jack: ''I write on behalf of more than 20,000 UK Samaritan volunteers who turn out day and night to be there on the line for the ever-growing number of despairing or suicidal people who seem to have nobody to turn to.

''We don't raise millions for research, but if a cash value were put on our unpaid and unsocial hours, surely the Samaritans would be rated among the biggest UK charities - and worth a mention?'' That's exactly why we've mentioned it. Anyone interested in becoming a volunteer should phone 0345 909 090.

AS MORE families convert to pedal power, a timely warning from Rospa about heading off safely. Every year, they remind Checklist, thousands of cyclists are hurt in accidents, with head injuries accounting for more than half the 200 deaths.

When choosing a cycle helmet, measure the head circumference about an inch above the eyebrows for a snug fit. Ensure that the helmet has a CE mark and meets recognised BS standards or Snell B 95. If it's too loose, use the pads provided or straps to get a close fit. Straps should go round the ears, not over them, with the buckle fastened just under the chin.

For a detailed leaflet, send an SAE to Rospa, Edgbaston Park, 353 Bristol Road, Birmingham, B5 7ST.

FAMILIES who fancy delving into their past are invited to consult the records at the Registrar's office, 22 Park Circus, Glasgow. Just #13 a day buys access to parish registers, census returns from 1841, and other records microfiched for easy access.

''We get lots of visitors from as far away as Australia and America wanting to trace relatives who hailed from these parts,'' says chief registrar Robert Sneddon. The more information you can take with you the better - especially birth places of parents and grandparents. For details phone 0141 287 8364.

In the East of Scotland, Edinburgh Central Library, with its long opening hours and extensive genealogical collections, is the place to trace ancestors. Gravestone records held at its Scottish Library may also provide useful clues. Details from 0131 225 5584.

Baby Talk: a mother and baby club launched by Huggies, makers of nappies and practice pants, offers a helping hand through pregnancy and beyond.

Every few months, from pregnancy to the active toddler stage, Huggies will send top tips and valuable information to mothers and mothers- to-be, with money-saving offers. For details of free membership write to Huggies, Mother & Baby Club, Dept 2099, Snowdon Drive, Winterhill, Milton Keynes MK6 1HW.