"Mares' tails and mackerel scales
Make lofty ships carry low sails."

This rather obscure, old saying forecasts a windy day when certain types of clouds are in the sky.
Four main types of clouds were classified in 1803 by an Englishman, Luke Howard, who gave each group a Latin name. The wispy, highest clouds he called Cirrus, These clouds are also known as "mare's tails" and are often forerunners of a storm. Mound-like, billowy clouds he called Cumulus. The term "mackerel scales" refers to Alto-Cumulus, the highest of the Cumulus type. Like "mare's tails" these too are often forerunners of a storm. He gave the name Stratus to layered clouds and Nimbus to dark rain clouds.

For many hundreds of years farmers relied on traditional sayings. But modern weather watchers and meteorologists rely little on old lore derived from experience and instead rely on experimental data and information collected and analyzed using new technologies. Among new technologies being developed is one that addresses what people all over the world so often want to do - change the weather!

In 1946 laboratory research to create artificial clouds in a chilled chamber suggested that certain techniques applied to clouds under the right conditions might induce rain. Field experiments in the 1950's were carried out by Vincent Schaefer and Irving Langmuir who dropped dry ice pellets from an airplane into a cloud. The basis for their experiment depended upon the fact that rain is formed in clouds when moisture collects around tiny particles.

Cloud seeding experiments continue in the 2000s with silver iodide as well as dry ice being delivered into clouds from rocket launchers on the ground as well as from planes.

The results are considered by many scientists to be inconclusive because success is not assured and it is not possible to say with any certainty that it would not have rained anyway!

Stumper Questions:

1. In which of these circumstances has cloud seeding not been used?

a. The weakening of a hurricane.

b. Reduction of the size of hailstones.

c. Dissipation of cool fogs.

d. Turning the Ho Chi Minh Trail into impassable muds.

e. Cooling volcanic lava.

2. What is the serious ethical question that must be considered if rainmaking becomes a more successful strategy?